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Versions: (RFC 4646) 00 01 02 03 04 05 06 07
08 09 10 11 12 13 14 15 16 17 18 19
20 21 22 23 RFC 5646
Network Working Group A. Phillips, Ed.
Internet-Draft Lab126
Obsoletes: 4646 (if approved) M. Davis, Ed.
Intended status: BCP Google
Expires: November 17, 2008 May 16, 2008
Tags for Identifying Languages
draft-ietf-ltru-4646bis-14
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Abstract
This document describes the structure, content, construction, and
semantics of language tags for use in cases where it is desirable to
indicate the language used in an information object. It also
describes how to register values for use in language tags and the
creation of user-defined extensions for private interchange.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. The Language Tag . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Language Subtag Sources and Interpretation . . . . . . . . 8
2.2.1. Primary Language Subtag . . . . . . . . . . . . . . . 9
2.2.2. Extended Language Subtags . . . . . . . . . . . . . . 11
2.2.3. Script Subtag . . . . . . . . . . . . . . . . . . . . 11
2.2.4. Region Subtag . . . . . . . . . . . . . . . . . . . . 12
2.2.5. Variant Subtags . . . . . . . . . . . . . . . . . . . 14
2.2.6. Extension Subtags . . . . . . . . . . . . . . . . . . 15
2.2.7. Private Use Subtags . . . . . . . . . . . . . . . . . 17
2.2.8. Grandfathered Registrations . . . . . . . . . . . . . 17
2.2.9. Classes of Conformance . . . . . . . . . . . . . . . . 18
3. Registry Format and Maintenance . . . . . . . . . . . . . . . 20
3.1. Format of the IANA Language Subtag Registry . . . . . . . 20
3.1.1. File Format . . . . . . . . . . . . . . . . . . . . . 20
3.1.2. Record Definitions . . . . . . . . . . . . . . . . . . 21
3.1.3. Subtag and Tag Fields . . . . . . . . . . . . . . . . 24
3.1.4. Description Field . . . . . . . . . . . . . . . . . . 24
3.1.5. Deprecated Field . . . . . . . . . . . . . . . . . . . 25
3.1.6. Preferred-Value Field . . . . . . . . . . . . . . . . 25
3.1.7. Prefix Field . . . . . . . . . . . . . . . . . . . . . 27
3.1.8. Suppress-Script Field . . . . . . . . . . . . . . . . 27
3.1.9. Macrolanguage Field . . . . . . . . . . . . . . . . . 28
3.1.10. Comments Field . . . . . . . . . . . . . . . . . . . . 29
3.2. Language Subtag Reviewer . . . . . . . . . . . . . . . . . 29
3.3. Maintenance of the Registry . . . . . . . . . . . . . . . 30
3.4. Stability of IANA Registry Entries . . . . . . . . . . . . 30
3.5. Registration Procedure for Subtags . . . . . . . . . . . . 34
3.6. Possibilities for Registration . . . . . . . . . . . . . . 38
3.7. Extensions and the Extensions Registry . . . . . . . . . . 41
3.8. Update of the Language Subtag Registry . . . . . . . . . . 43
4. Formation and Processing of Language Tags . . . . . . . . . . 45
4.1. Choice of Language Tag . . . . . . . . . . . . . . . . . . 45
4.1.1. Tagging Encompassed Languages . . . . . . . . . . . . 49
4.2. Meaning of the Language Tag . . . . . . . . . . . . . . . 50
4.3. Lists of Languages . . . . . . . . . . . . . . . . . . . . 52
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4.4. Length Considerations . . . . . . . . . . . . . . . . . . 53
4.4.1. Working with Limited Buffer Sizes . . . . . . . . . . 53
4.4.2. Truncation of Language Tags . . . . . . . . . . . . . 54
4.5. Canonicalization of Language Tags . . . . . . . . . . . . 55
4.6. Considerations for Private Use Subtags . . . . . . . . . . 57
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 58
5.1. Language Subtag Registry . . . . . . . . . . . . . . . . . 58
5.2. Extensions Registry . . . . . . . . . . . . . . . . . . . 59
6. Security Considerations . . . . . . . . . . . . . . . . . . . 61
7. Character Set Considerations . . . . . . . . . . . . . . . . . 62
8. Changes from RFC 4646 . . . . . . . . . . . . . . . . . . . . 63
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 67
9.1. Normative References . . . . . . . . . . . . . . . . . . . 67
9.2. Informative References . . . . . . . . . . . . . . . . . . 68
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 70
Appendix B. Examples of Language Tags (Informative) . . . . . . . 71
Appendix C. Examples of Registration Forms . . . . . . . . . . . 74
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 76
Intellectual Property and Copyright Statements . . . . . . . . . . 77
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1. Introduction
Human beings on our planet have, past and present, used a number of
languages. There are many reasons why one would want to identify the
language used when presenting or requesting information.
A user's language preferences often need to be identified so that
appropriate processing can be applied. For example, the user's
language preferences in a Web browser can be used to select Web pages
appropriately. Language preferences can also be used to select among
tools (such as dictionaries) to assist in the processing or
understanding of content in different languages.
In addition, knowledge about the particular language used by some
piece of information content might be useful or even required by some
types of processing; for example, spell-checking, computer-
synthesized speech, Braille transcription, or high-quality print
renderings.
One means of indicating the language used is by labeling the
information content with an identifier or "tag". These tags can be
used to specify user preferences when selecting information content,
or for labeling additional attributes of content and associated
resources.
Tags can also be used to indicate additional language attributes of
content. For example, indicating specific information about the
dialect, writing system, or orthography used in a document or
resource may enable the user to obtain information in a form that
they can understand, or it can be important in processing or
rendering the given content into an appropriate form or style.
This document specifies a particular identifier mechanism (the
language tag) and a registration function for values to be used to
form tags. It also defines a mechanism for private use values and
future extension.
This document replaces [RFC4646], which replaced [RFC3066] and its
predecessor [RFC1766]. For a list of changes in this document, see
Section 8.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. The Language Tag
Language tags are used to help identify languages, whether spoken,
written, signed, or otherwise signaled, for the purpose of
communication. This includes constructed and artificial languages,
but excludes languages not intended primarily for human
communication, such as programming languages.
2.1. Syntax
The language tag is composed of one or more parts, known as
"subtags". Each subtag consists of a sequence of alphanumeric
characters. Subtags are distinguished and separated from one another
by a hyphen ("-", ABNF [RFC5234] %x2D). Usually a language tag
contains a "primary language" subtag, followed by a (possibly empty)
series of subsequent subtags, each of which refines or narrows the
range of languages identified by the overall tag.
Most subtags are distinguished by length, position in the tag, and
content: subtags can be recognized solely by these features. This
makes it possible to construct a parser that can extract and assign
some semantic information to the subtags, even if the specific subtag
values are not recognized. Thus, a parser need not have a list of
valid tags or subtags (that is, a copy of some version of the IANA
Language Subtag Registry) in order to perform common searching and
matching operations. The grandfathered tags registered under RFC
3066 [RFC3066], a fixed list that can never change, are the only
exception to this ability to infer meaning from subtag structure.
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The syntax of the language tag in ABNF [RFC5234] is:
Language-Tag = langtag
/ privateuse ; private use tag
/ irregular ; tags grandfathered by rule
langtag = (language
["-" script]
["-" region]
*("-" variant)
*("-" extension)
["-" privateuse])
language = 2*3ALPHA ; shortest ISO 639 code
/ 4ALPHA ; reserved for future use
/ 5*8ALPHA ; registered language subtag
script = 4ALPHA ; ISO 15924 code
region = 2ALPHA ; ISO 3166-1 code
/ 3DIGIT ; UN M.49 code
variant = 5*8alphanum ; registered variants
/ (DIGIT 3alphanum)
extension = singleton 1*("-" (2*8alphanum))
singleton = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT
; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9"
; Single alphanumerics
; "x" is reserved for private use
privateuse = "x" 1*("-" (1*8alphanum))
irregular = "en-GB-oed" / "i-ami" / "i-bnn" / "i-default"
/ "i-enochian" / "i-hak" / "i-klingon" / "i-lux"
/ "i-mingo" / "i-navajo" / "i-pwn" / "i-tao"
/ "i-tay" / "i-tsu" / "no-bok" / "no-nyn"
/ "sgn-BE-FR" / "sgn-BE-NL" / "sgn-CH-DE" / "zh-cmn"
/ "zh-cmn-Hans" / "zh-cmn-Hant" / "zh-gan"
/ "zh-min" / "zh-min-nan" / "zh-wuu" / "zh-yue"
alphanum = (ALPHA / DIGIT) ; letters and numbers
Figure 1: Language Tag ABNF
All subtags have a maximum length of eight characters and whitespace
is not permitted in a language tag. There is a subtlety in the ABNF
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production 'variant': variants starting with a digit MAY be four
characters long, while those starting with a letter MUST be at least
five characters long. For examples of language tags, see Appendix B.
Note Well: the ABNF syntax does not distinguish between upper and
lowercase. The appearance of upper and lowercase letters in the
various ABNF productions above do not affect how implementations
interpret tags. That is, the tag "I-AMI" matches the item "i-ami" in
the 'irregular' production. At all times, the tags and their
subtags, including private use and extensions, are to be treated as
case insensitive: there exist conventions for the capitalization of
some of the subtags, but these MUST NOT be taken to carry meaning.
For example:
o [ISO639-1] recommends that language codes be written in lowercase
('mn' Mongolian).
o [ISO3166-1] recommends that country codes be capitalized ('MN'
Mongolia).
o [ISO15924] recommends that script codes use lowercase with the
initial letter capitalized ('Cyrl' Cyrillic).
However, in the tags defined by this document, the uppercase US-ASCII
letters in the range 'A' through 'Z' are considered equivalent and
mapped directly to their US-ASCII lowercase equivalents in the range
'a' through 'z'. Thus, the tag "mn-Cyrl-MN" is not distinct from
"MN-cYRL-mn" or "mN-cYrL-Mn" (or any other combination), and each of
these variations conveys the same meaning: Mongolian written in the
Cyrillic script as used in Mongolia.
Although case distinctions do not carry meaning in language tags,
consistent formatting and presentation of the tags will aid users.
The format of the tags and subtags in the registry is RECOMMENDED.
In this format, all subtags, including all those following singletons
(that is, in extension or private-use sequences) are in lowercase.
The exceptions to this are: all other non-initial two-letter subtags
are uppercase and all other non-initial four-letter subtags are
titlecase.
Note that although [RFC5234] refers to octets, the language tags
described in this document are sequences of characters from the US-
ASCII [ISO646] repertoire. Language tags MAY be used in documents
and applications that use other encodings, so long as these encompass
the US-ASCII repertoire. An example of this would be an XML document
that uses the UTF-16LE [RFC2781] encoding of [Unicode].
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2.2. Language Subtag Sources and Interpretation
The namespace of language tags and their subtags is administered by
the Internet Assigned Numbers Authority (IANA) [RFC2860] according to
the rules in Section 5 of this document. The Language Subtag
Registry maintained by IANA is the source for valid subtags: other
standards referenced in this section provide the source material for
that registry.
Terminology used in this document:
o "Tag" refers to a complete language tag, such as "sr-Latn-RS" or
"az-Arab-IR". Examples of tags in this document are enclosed in
double-quotes ("en-US").
o "Subtag" refers to a specific section of a tag, delimited by
hyphen, such as the subtag 'Hant' in "zh-Hant-CN". Examples of
subtags in this document are enclosed in single quotes ('Hant').
o "Code" refers to values defined in external standards (and which
are used as subtags in this document). For example, 'Hant' is an
[ISO15924] script code that was used to define the 'Hant' script
subtag for use in a language tag. Examples of codes in this
document are enclosed in single quotes ('en', 'Hant').
The definitions in this section apply to the various subtags within
the language tags defined by this document, excepting those
"grandfathered" tags defined in Section 2.2.8.
Language tags are designed so that each subtag type has unique length
and content restrictions. These make identification of the subtag's
type possible, even if the content of the subtag itself is
unrecognized. This allows tags to be parsed and processed without
reference to the latest version of the underlying standards or the
IANA registry and makes the associated exception handling when
parsing tags simpler.
Subtags in the IANA registry that do not come from an underlying
standard can only appear in specific positions in a tag.
Specifically, they can only occur as primary language subtags or as
variant subtags.
Note that sequences of private use and extension subtags MUST occur
at the end of the sequence of subtags and MUST NOT be interspersed
with subtags defined elsewhere in this document.
Single-letter and single-digit subtags are reserved for current or
future use. These include the following current uses:
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o The single-letter subtag 'x' is reserved to introduce a sequence
of private use subtags. The interpretation of any private use
subtags is defined solely by private agreement and is not defined
by the rules in this section or in any standard or registry
defined in this document.
o All other single-letter subtags are reserved to introduce
standardized extension subtag sequences as described in
Section 3.7.
o The single-letter subtag 'i' is used by some grandfathered tags,
such as "i-default", where it always appears in the first position
and cannot be confused with an extension.
2.2.1. Primary Language Subtag
The primary language subtag is the first subtag in a language tag
(with the exception of private use and certain grandfathered tags)
and cannot be omitted. The following rules apply to the primary
language subtag:
1. All two-character primary language subtags were defined in the
IANA registry according to the assignments found in the standard
ISO 639 Part 1, "ISO 639-1:2002, Codes for the representation of
names of languages -- Part 1: Alpha-2 code" [ISO639-1], or using
assignments subsequently made by the ISO 639-1 registration
authority (RA) or governing standardization bodies.
2. All three-character primary language subtags were defined in the
IANA registry according to the assignments found in either ISO
639 Part 2, "ISO 639-2:1998 - Codes for the representation of
names of languages -- Part 2: Alpha-3 code - edition 1"
[ISO639-2], ISO 639 Part 3, "Codes for the representation of
names of languages -- Part 3: Alpha-3 code for comprehensive
coverage of languages" [ISO639-3], or assignments subsequently
made by the relevant ISO 639 registration authorities or
governing standardization bodies.
3. The subtags in the range 'qaa' through 'qtz' are reserved for
private use in language tags. These subtags correspond to codes
reserved by ISO 639-2 for private use. These codes MAY be used
for non-registered primary language subtags (instead of using
private use subtags following 'x-'). Please refer to Section 4.6
for more information on private use subtags.
4. All four-character language subtags are reserved for possible
future standardization.
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5. All language subtags of 5 to 8 characters in length in the IANA
registry were defined via the registration process in Section 3.5
and MAY be used to form the primary language subtag. At the time
this document was created, there were no examples of this kind of
subtag and future registrations of this type will be discouraged:
primary languages are strongly RECOMMENDED for registration with
ISO 639, and proposals rejected by ISO 639/RA-JAC will be closely
scrutinized before they are registered with IANA.
6. The single-character subtag 'x' as the primary subtag indicates
that the language tag consists solely of subtags whose meaning is
defined by private agreement. For example, in the tag "x-fr-CH",
the subtags 'fr' and 'CH' SHOULD NOT be taken to represent the
French language or the country of Switzerland (or any other value
in the IANA registry) unless there is a private agreement in
place to do so. See Section 4.6.
7. The single-character subtag 'i' is used by some grandfathered
tags (see Section 2.2.8) such as "i-klingon" and "i-bnn". (Other
grandfathered tags have a primary language subtag in their first
position.)
8. Other values MUST NOT be assigned to the primary subtag except by
revision or update of this document.
Note: For languages that have both an ISO 639-1 two-character code
and a three character code assigned by either ISO 639-2 or ISO 639-3,
only the ISO 639-1 two-character code is defined in the IANA
registry.
Note: For languages that have no ISO 639-1 two-character code and for
which the ISO 639-2/T (Terminology) code and the ISO 639-2/B
(Bibliographic) codes differ, only the Terminology code is defined in
the IANA registry. At the time this document was created, all
languages that had both kinds of three-character code were also
assigned a two-character code; it is expected that future assignments
of this nature will not occur.
Note: To avoid problems with versioning and subtag choice as
experienced during the transition between RFC 1766 and RFC 3066, as
well as the canonical nature of subtags defined by this document, the
ISO 639 Registration Authority Joint Advisory Committee (ISO 639/
RA-JAC) has included the following statement in [iso639.prin]:
"A language code already in ISO 639-2 at the point of freezing ISO
639-1 shall not later be added to ISO 639-1. This is to ensure
consistency in usage over time, since users are directed in
Internet applications to employ the alpha-3 code when an alpha-2
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code for that language is not available."
In order to avoid instability in the canonical form of tags, if a
two-character code is added to ISO 639-1 for a language for which a
three-character code was already included in either ISO 639-2 or ISO
639-3, the two-character code MUST NOT be registered. See
Section 3.4.
For example, if some content were tagged with 'haw' (Hawaiian), which
currently has no two-character code, the tag would not be invalidated
if ISO 639-1 were to assign a two-character code to the Hawaiian
language at a later date.
Note: An example of independent primary language subtag registration
might include: one of the grandfathered IANA registrations is
"i-enochian". The subtag 'enochian' could be registered in the IANA
registry as a primary language subtag (assuming that ISO 639 does not
register this language first), making tags such as "enochian-AQ" and
"enochian-Latn" valid.
2.2.2. Extended Language Subtags
[RFC4646] contained an additional type of subtag called the 'extended
language subtag' to allow for certain kinds of compatibility mappings
which ultimately were not used. These subtags were reserved for
future use and ultimately removed from the ABNF. They MUST NOT be
registered or used to form language tags. See also Section 2.2.9 for
a discussion of the consequences of removing the 'extlang' production
from grammar.
Note: a few grandfathered tags (Section 2.2.8) matched the 'extlang'
production in RFC 4646, and thus were not considered 'irregular'.
These tags are still valid and were added to the 'irregular'
production in the ABNF.
2.2.3. Script Subtag
Script subtags are used to indicate the script or writing system
variations that distinguish the written forms of a language or its
dialects. The following rules apply to the script subtags:
1. Script subtags MUST follow the primary language subtag and MUST
precede any other type of subtag.
2. All four-character subtags were defined according to
[ISO15924]--"Codes for the representation of the names of
scripts": alpha-4 script codes, or subsequently assigned by the
ISO 15924 registration authority or governing standardization
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bodies, denoting the script or writing system used in conjunction
with this language.
3. The script subtags 'Qaaa' through 'Qabx' are reserved for private
use in language tags. These subtags correspond to codes reserved
by ISO 15924 for private use. These codes MAY be used for non-
registered script values. Please refer to Section 4.6 for more
information on private use subtags.
4. Script subtags MUST NOT be registered using the process in
Section 3.5 of this document. Variant subtags MAY be considered
for registration for that purpose.
5. There MUST be at most one script subtag in a language tag, and
the script subtag SHOULD be omitted when it adds no
distinguishing value to the tag or when the primary language
subtag's record includes a Suppress-Script field listing the
applicable script subtag.
Example: "sr-Latn" represents Serbian written using the Latin script.
2.2.4. Region Subtag
Region subtags are used to indicate linguistic variations associated
with or appropriate to a specific country, territory, or region.
Typically, a region subtag is used to indicate regional dialects or
usage, or region-specific spelling conventions. A region subtag can
also be used to indicate that content is expressed in a way that is
appropriate for use throughout a region, for instance, Spanish
content tailored to be useful throughout Latin America.
The following rules apply to the region subtags:
1. Region subtags MUST follow any language or script subtags and
MUST precede any other type of subtag.
2. All two-character subtags following the primary subtag were
defined in the IANA registry according to the assignments found
in [ISO3166-1] ("Codes for the representation of names of
countries and their subdivisions -- Part 1: Country codes") using
the list of alpha-2 country codes, or using assignments
subsequently made by the ISO 3166-1 maintenance agency or
governing standardization bodies. In addition, the codes that
are "exceptionally reserved" (as opposed to "assigned") in ISO
3166-1 were also defined in the registry, with the exception of
'UK', which is an exact synonym for the assigned code 'GB'.
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3. All three-character subtags consisting of digit (numeric)
characters following the primary subtag were defined in the IANA
registry according to the assignments found in UN Standard
Country or Area Codes for Statistical Use [UN_M.49] or
assignments subsequently made by the governing standards body.
Note that not all of the UN M.49 codes are defined in the IANA
registry. The following rules define which codes are entered
into the registry as valid subtags:
A. UN numeric codes assigned to 'macro-geographical
(continental)' or sub-regions MUST be registered in the
registry. These codes are not associated with an assigned
ISO 3166-1 alpha-2 code and represent supra-national areas,
usually covering more than one nation, state, province, or
territory.
B. UN numeric codes for 'economic groupings' or 'other
groupings' MUST NOT be registered in the IANA registry and
MUST NOT be used to form language tags.
C. When ISO 3166-1 reassigns a code formerly used for one
country or area to another country or area and that code
already is present in the registry, the UN numeric code for
that country or area MUST be registered in the registry as
described in Section 3.4 and MUST be used to form language
tags that represent the country or region for which it is
defined (rather than the recycled ISO 3166-1 code).
D. UN numeric codes for countries or areas for which there is an
associated ISO 3166-1 alpha-2 code in the registry MUST NOT
be entered into the registry and MUST NOT be used to form
language tags. Note that the ISO 3166-based subtag in the
registry MUST actually be associated with the UN M.49 code in
question.
E. UN numeric codes and ISO 3166-1 alpha-2 codes for countries
or areas listed as eligible for registration in [RFC4645] but
not presently registered MAY be entered into the IANA
registry via the process described in Section 3.5. Once
registered, these codes MAY be used to form language tags.
F. All other UN numeric codes for countries or areas that do not
have an associated ISO 3166-1 alpha-2 code MUST NOT be
entered into the registry and MUST NOT be used to form
language tags. For more information about these codes, see
Section 3.4.
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4. Note: The alphanumeric codes in Appendix X of the UN document
MUST NOT be entered into the registry and MUST NOT be used to
form language tags. (At the time this document was created,
these values matched the ISO 3166-1 alpha-2 codes.)
5. There MUST be at most one region subtag in a language tag and the
region subtag MAY be omitted, as when it adds no distinguishing
value to the tag.
6. The region subtags 'AA', 'QM'-'QZ', 'XA'-'XZ', and 'ZZ' are
reserved for private use in language tags. These subtags
correspond to codes reserved by ISO 3166 for private use. These
codes MAY be used for private use region subtags (instead of
using a private use subtag sequence). Please refer to
Section 4.6 for more information on private use subtags.
"de-AT" represents German ('de') as used in Austria ('AT').
"sr-Latn-RS" represents Serbian ('sr') written using Latin script
('Latn') as used in Serbia ('RS').
"es-419" represents Spanish ('es') appropriate to the UN-defined
Latin America and Caribbean region ('419').
2.2.5. Variant Subtags
Variant subtags are used to indicate additional, well-recognized
variations that define a language or its dialects that are not
covered by other available subtags. The following rules apply to the
variant subtags:
1. Variant subtags MUST follow any language, script, or region
subtags, but MUST precede any extension or private use subtag
sequences.
2. Variant subtags, as a collection, are not associated with any
particular external standard. The meaning of variant subtags in
the registry is defined in the course of the registration process
defined in Section 3.5. Note that any particular variant subtag
might be associated with some external standard. However,
association with a standard is not required for registration.
3. More than one variant MAY be used to form the language tag.
4. Variant subtags MUST be registered with IANA according to the
rules in Section 3.5 of this document before being used to form
language tags. In order to distinguish variants from other types
of subtags, registrations MUST meet the following length and
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content restrictions:
1. Variant subtags that begin with a letter (a-z, A-Z) MUST be
at least five characters long.
2. Variant subtags that begin with a digit (0-9) MUST be at
least four characters long.
5. The same variant subtag MUST NOT be used more than once within a
language tag.
* For example, the tag "de-DE-1901-1901" is not valid.
Variant subtag records in the language subtag registry MAY include
one or more 'Prefix' fields. The 'Prefix' indicates the language tag
or tags that would make a suitable prefix (with other subtags, as
appropriate) in forming a language tag with the variant. That is,
each of the subtags in the prefix SHOULD appear, in order, before the
variant. For example, the subtag 'nedis' has a Prefix of "sl",
making it suitable for forming language tags such as "sl-nedis" and
"sl-IT-nedis", but not suitable for use in a tag such as "zh-nedis"
or "it-IT-nedis".
"sl-nedis" represents the Natisone or Nadiza dialect of Slovenian.
"de-CH-1996" represents German as used in Switzerland and as written
using the spelling reform beginning in the year 1996 C.E.
Most variants that share a prefix are mutually exclusive. For
example, the German orthographic variations '1996' and '1901' SHOULD
NOT be used in the same tag, as they represent the dates of different
spelling reforms. A variant that can meaningfully be used in
combination with another variant SHOULD include a 'Prefix' field in
its registry record that lists that other variant. For example, if
another German variant 'example' were created that made sense to use
with '1996', then 'example' should include two Prefix fields: "de"
and "de-1996".
2.2.6. Extension Subtags
Extensions provide a mechanism for extending language tags for use in
various applications. They are intended to identify information
which is commonly used in association with languages or language
tags, but which is not part of language identification. See
Section 3.7. The following rules apply to extensions:
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1. An extension MUST follow at least a primary language subtag.
That is, a language tag cannot begin with an extension.
Extensions extend language tags, they do not override or replace
them. For example, "a-value" is not a well-formed language tag,
while "de-a-value" is.
2. Extension subtags are separated from the other subtags defined
in this document by a single-character subtag ("singleton").
The singleton MUST be one allocated to a registration authority
via the mechanism described in Section 3.7 and MUST NOT be the
letter 'x', which is reserved for private use subtag sequences.
3. Note: Private use subtag sequences starting with the singleton
subtag 'x' are described in Section 2.2.7 below.
4. Each singleton subtag MUST appear at most one time in each tag
(other than as a private use subtag). That is, singleton
subtags MUST NOT be repeated. For example, the tag "en-a-bbb-a-
ccc" is invalid because the subtag 'a' appears twice. Note that
the tag "en-a-bbb-x-a-ccc" is valid because the second
appearance of the singleton 'a' is in a private use sequence.
5. Extension subtags MUST meet all of the requirements for the
content and format of subtags defined in this document.
6. Extension subtags MUST meet whatever requirements are set by the
document that defines their singleton prefix and whatever
requirements are provided by the maintaining authority.
7. Each extension subtag MUST be from two to eight characters long
and consist solely of letters or digits, with each subtag
separated by a single '-'.
8. Each singleton MUST be followed by at least one extension
subtag. For example, the tag "tlh-a-b-foo" is invalid because
the first singleton 'a' is followed immediately by another
singleton 'b'.
9. Extension subtags MUST follow all language, script, region, and
variant subtags in a tag.
10. All subtags following the singleton and before another singleton
are part of the extension. Example: In the tag "fr-a-Latn", the
subtag 'Latn' does not represent the script subtag 'Latn'
defined in the IANA Language Subtag Registry. Its meaning is
defined by the extension 'a'.
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11. In the event that more than one extension appears in a single
tag, the tag SHOULD be canonicalized as described in
Section 4.5.
For example, if the prefix singleton 'r' and the shown subtags were
defined, then the following tag would be a valid example: "en-Latn-
GB-boont-r-extended-sequence-x-private"
2.2.7. Private Use Subtags
Private use subtags are used to indicate distinctions in language
important in a given context by private agreement. The following
rules apply to private use subtags:
1. Private use subtags are separated from the other subtags defined
in this document by the reserved single-character subtag 'x'.
2. Private use subtags MUST conform to the format and content
constraints defined in the ABNF for all subtags.
3. Private use subtags MUST follow all language, script, region,
variant, and extension subtags in the tag. Another way of saying
this is that all subtags following the singleton 'x' MUST be
considered private use. Example: The subtag 'US' in the tag "en-
x-US" is a private use subtag.
4. A tag MAY consist entirely of private use subtags.
5. No source is defined for private use subtags. Use of private use
subtags is by private agreement only.
6. Private use subtags are NOT RECOMMENDED where alternatives exist
or for general interchange. See Section 4.6 for more information
on private use subtag choice.
For example: The Unicode Consortium defines a set of private use
extensions in LDML ([UTS35], Locale Data Markup Language, the Unicode
standard for defining locale data) such as in the tag "es-419-x-ldml-
collatio-traditio", which indicates Latin American Spanish with
traditional order for sorted lists.
2.2.8. Grandfathered Registrations
Prior to RFC 4646, whole language tags were registered according to
the rules in RFC 1766 and/or RFC 3066. These registered tags
maintain their validity. Of those tags, those that were made
obsolete or redundant by the advent of RFC 4646, by this document, or
by subsequent registration of subtags are maintained in the registry
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in records as "redundant" records. Those tags that do not match the
'langtag' production in the ABNF in this document or that contain
subtags that do not individually appear in the registry are
maintained in the registry in records of the "grandfathered" type.
Grandfathered tags contain one or more subtags that are not defined
in the Language Subtag Registry (see Section 3). Redundant tags
consist entirely of subtags defined above and whose independent
registration was superseded by [RFC4646]. For more information see
Section 3.8.
Some grandfathered tags are "regular" in that they match the
'langtag' production in Figure 1. In some cases, these tags could
become redundant if their (currently unregistered) subtags were to be
registered (as variants, for example). In other cases, although the
subtags match the language tag pattern, the meaning assigned to the
various subtags is prohibited by rules elsewhere in this document.
Those tags can never become redundant.
The remaining grandfathered tags are "irregular" and do not match the
'langtag' production. These are listed in the 'irregular' production
in Figure 1. These grandfathered tags can never become redundant.
Many of these tags have been superseded by other registrations: their
record contains a Preferred-Value field that really ought to be used
to form language tags representing that value.
2.2.9. Classes of Conformance
Implementations sometimes need to describe their capabilities with
regard to the rules and practices described in this document. Tags
can be checked or verified in a number of ways, but two particular
classes of tag conformance are formally defined here.
A tag is considered "well-formed" if it conforms to the ABNF
(Section 2.1). Note that irregular grandfathered tags are now listed
in the 'irregular' production.
A tag is considered "valid" if it satisfies these conditions:
o The tag is well-formed.
o The tag is either a grandfathered tag, or all of its language,
script, region, and variant subtags appear in the IANA language
subtag registry as of the particular registry date.
o There are no duplicate singleton (extension) subtags and no
duplicate variant subtags.
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Note that a tag's validity depends on the date of the registry used
to validate the tag. A more recent copy of the registry might
contain a subtag that an older version does not.
A tag is considered "valid" for a given extension (Section 3.7) (as
of a particular version, revision, and date) if it meets the criteria
for "valid" above and also satisfies this condition:
Each subtag used in the extension part of the tag is valid
according to the extension.
Some older implementations consider a tag "well-formed" if it matches
the ABNF in [RFC4646]. In that version, a well-formed tag could
contain a sequence matching the obsolete 'extlang' production. Other
than a few grandfathered tags (which are handled separately), no
valid tags have ever matched that pattern. The difference between
that ABNF and Figure 1 is that the language production is replaced as
follows:
obs-primary-language = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code
/ 4ALPHA ; reserved for future use
/ 5*8ALPHA ; registered language subtag
extlang = *3("-" 3ALPHA) ; removed in this version
Figure 2: Obsolete Language ABNF
Older language tag implementations sometimes reference [RFC3066].
Again, all valid tags under that version also match this document's
language tag ABNF. However, a wider array of tags could be
considered "well-formed" under that document. The 'Language-Tag'
production used in that document matches the following:
obs-language-tag = primary-subtag *( "-" subtag )
primary-subtag = 1*8ALPHA
subtag = 1*8(ALPHA / DIGIT)
Figure 3: RFC 3066 Language Tag Syntax
Language tags may be well-formed in terms of syntax but not valid in
terms of content. Users MUST NOT assign and use their own subtags,
other than private-use sequences (such as "en-x-personal") or by
using subtags designated as private-use in the registry (such as
"no-QQ", where 'QQ' is one of a range of private-use ISO 3166-1
codes). Not only is such assignment nonconformant, it also risks
collision with a future possible assignment. The private use subtags
and sequences are designed for this case.
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3. Registry Format and Maintenance
This section defines the Language Subtag Registry and the maintenance
and update procedures associated with it, as well as a registry for
extensions to language tags (Section 3.7).
The Language Subtag Registry contains a comprehensive list of all of
the subtags valid in language tags. This allows implementers a
straightforward and reliable way to validate language tags. The
Language Subtag Registry will be maintained so that, except for
extension subtags, it is possible to validate all of the subtags that
appear in a language tag under the provisions of this document or its
revisions or successors. In addition, the meaning of the various
subtags will be unambiguous and stable over time. (The meaning of
private use subtags, of course, is not defined by the IANA registry.)
3.1. Format of the IANA Language Subtag Registry
The IANA Language Subtag Registry ("the registry") is a machine-
readable file in the format described in this section, plus copies of
the registration forms approved in accordance with the process
described in Section 3.5.
Note: The existing registration forms for grandfathered and redundant
tags taken from RFC 3066 have been maintained as part of the obsolete
RFC 3066 registry. The subtags added to the registry by either
[RFC4645] or [registry-update] do not have separate registration
forms (so no forms are archived for these additions).
3.1.1. File Format
The registry consists of a series of records stored in the record-jar
format (described in [record-jar]). Each record, in turn, consists
of a series of fields that describe the various subtags and tags.
The registry is a Unicode [Unicode] text file, using the UTF-8
[RFC3629] character encoding.
Each field can be considered a single, logical line of Unicode
[Unicode] characters, comprising a field-name and a field-body
separated by a COLON character (%x3A). Each field is terminated by
the newline sequence CRLF. The text in each field MUST be in Unicode
Normalization Form C (NFC).
A collection of fields forms a 'record'. Records are separated by
lines containing only the sequence "%%" (%x25.25).
Although fields are logically a single line of text, each line of
text in the file format is limited to 72 bytes in length. To
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accommodate this, the field-body can be split into a multiple-line
representation; this is called "folding". Folding is done according
to customary conventions for line-wrapping. This is typically on
whitespace boundaries, but can occur between other characters when
the value does not include spaces, such as when a language does not
use whitespace between words. In any event, there MUST NOT be breaks
inside a multibyte UTF-8 sequence nor in the middle of a combining
character sequence. For more information, see [UAX14].
Although the file format uses the UTF-8 encoding, unless otherwise
indicated, fields are restricted to the printable characters from the
US-ASCII [ISO646] repertoire.
The format of the registry is described by the following ABNF (per
[RFC5234]):
registry = record *("%%" CRLF record)
record = 1*( field-name *SP ":" *SP field-body CRLF )
field-name = (ALPHA / DIGIT) [*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)]
field-body = *([[*SP CRLF] 1*SP] 1*CHARS)
CHARS = (%x21-10FFFF) ; Unicode code points
Figure 4: Registry Format ABNF
The sequence '..' (%x2E.2E) in a field-body denotes a range of
values. Such a range represents all subtags of the same length that
are in alphabetic or numeric order within that range, including the
values explicitly mentioned. For example 'a..c' denotes the values
'a', 'b', and 'c' and '11..13' denotes the values '11', '12', and
'13'.
All fields whose field-body contains a date value use the "full-date"
format specified in [RFC3339]. For example: "2004-06-28" represents
June 28, 2004, in the Gregorian calendar.
3.1.2. Record Definitions
There are three types of records in the registry: "File-Date",
"Subtag", and "Tag" records.
The first record in the registry is a "File-Date" record. This
record contains the single field whose field-name is "File-Date" (see
Figure 4). The field-body of this record contains the last
modification date of this copy of the registry, making it possible to
compare different versions of the registry. The registry on the IANA
website is the most current. Versions with an older date than that
one are not up-to-date.
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File-Date: 2004-06-28
%%
Figure 5: Example of the File-Date Record
Subsequent records represent either subtags or tags in the registry.
"Subtag" records contain a field with a field-name of "Subtag",
while, unsurprisingly, "Tag" records contain a field with a field-
name of "Tag". Each of the fields in each record MUST occur no more
than once, unless otherwise noted below. Each record MUST contain
the following fields:
o 'Type'
* Type's field-body MUST consist of one of the following strings:
"language", "script", "region", "variant", "grandfathered", and
"redundant" and denotes the type of tag or subtag.
o Either 'Subtag' or 'Tag'
* Subtag's field-body contains the subtag being defined. This
field MUST only appear in records of whose 'Type' has one of
these values: "language", "script", "region", or "variant".
* Tag's field-body contains a complete language tag. This field
MUST only appear in records whose 'Type' has one of these
values: "grandfathered" or "redundant". Note that the field-
body will always follow the 'grandfathered' production in the
ABNF in Section 2.1
o Description
* Description's field-body contains a non-normative description
of the subtag or tag.
o Added
* Added's field-body contains the date the record was registered
or, in the case of grandfathered or redundant tags, the date
the corresponding tag was registered under the rules of
[RFC1766] or [RFC3066].
Each record MAY also contain the following fields:
o Preferred-Value
* For fields of type 'script', 'region', and 'variant',
'Preferred-Value' contains the subtag of the same 'Type' that
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is preferred for forming the language tag.
* For fields of type 'language', 'Preferred-Value' contains the
primary language subtag that is preferred when forming the
language tag.
* For fields of type 'grandfathered' and 'redundant', 'Preferred-
Value' contains a canonical mapping to a complete language tag.
o Deprecated
* Deprecated's field-body contains the date the record was
deprecated. In some cases this value is before that of the
associated 'Added' field in the registry.
o Prefix
* Prefix's field-body contains a language tag with which this
subtag MAY be used to form a new language tag, perhaps with
other subtags as well. The Prefix's subtags appear before the
subtag. This field MUST only appear in records whose 'Type'
field-body is 'variant'. For example, the 'Prefix' for the
variant 'nedis' is 'sl', meaning that the tags "sl-nedis" and
"sl-IT-nedis" are appropriate while the tag "is-nedis" is not.
o Comments
* Comments's field-body contains additional information about the
subtag, as deemed appropriate for understanding the registry
and implementing language tags using the subtag or tag.
o Suppress-Script
* Suppress-Script's field-body contains a script subtag that
SHOULD NOT be used to form language tags with the associated
primary language subtag. This field MUST only appear in
records whose 'Type' field-body is 'language'. See
Section 4.1.
o Macrolanguage
* Macrolanguage's field-body contains a primary language subtag
defined by ISO 639 as a "macrolanguage" that encompasses this
language subtag. This field MUST only appear in records whose
'Type' field-body is 'language'.
Future versions of this document might add additional fields to the
registry, so implementations SHOULD ignore fields found in the
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registry that are not defined in this document.
3.1.3. Subtag and Tag Fields
The 'Subtag' field MUST NOT use uppercase letters to form the subtag,
with two exceptions. Subtags whose 'Type' field is 'script' (in
other words, subtags defined by ISO 15924) MUST use titlecase.
Subtags whose 'Type' field is 'region' (in other words, the non-
numeric region subtags defined by ISO 3166-1) MUST use all uppercase.
These exceptions mirror the use of case in the underlying standards.
Each subtag in the tags contained in a 'Tag' field MUST be formatted
using the rules in the preceding paragraph. That is, all subtags are
lowercase except for subtags that represent script or region codes.
3.1.4. Description Field
The field 'Description' contains a description of the tag or subtag
in the record. The 'Description' field MAY appear more than once per
record, that is, there can be multiple descriptions for a given
record. The 'Description' field MAY include the full range of
Unicode characters. At least one of the 'Description' fields MUST be
written or transcribed into the Latin script; additional
'Description' fields MAY also include a description in a non-Latin
script. Each 'Description' field MUST be unique, both within the
record in which it appears and for the collection of records of the
same type. Moreover, formatting variations of the same description
MUST NOT occur in that specific record or in any other record of the
same type. For example, while the ISO 639-1 code 'fy' contains both
the descriptions "Western Frisian" and "Frisian, Western", only one
of these descriptions appears in the registry.
The 'Description' field is used for identification purposes. It
doesn't necessarily represent the actual native name of the item in
the record, nor are any of the descriptions guaranteed to be in any
particular language (such as English or French, for example).
For subtags taken from a source standard (such as ISO 639 or ISO
15924), the 'Description' value(s) SHOULD also be taken from the
source standard. Multiple descriptions in the source standard MUST
be split into separate 'Description' fields. The source standard's
descriptions MAY be edited, either prior to insertion or via the
registration process. For fields of type 'language', the first
'Description' field appearing in the Registry corresponds to the
Reference Name assigned by ISO 639-3. This helps facilitate cross-
referencing between ISO 639 and the registry.
When creating or updating a record due to the action of one of the
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source standards, the Language Subtag Reviewer SHOULD remove
duplicate or redundant descriptions and MAY edit descriptions to
correct irregularities in formatting (such as misspellings,
inappropriate apostrophes or other punctuation, or excessive or
missing spaces) prior to submitting the proposed record to the ietf-
languages list.
Note: Descriptions in registry entries that correspond to ISO 639,
ISO 15924, ISO 3166-1, or UN M.49 codes are intended only to indicate
the meaning of that identifier as defined in the source standard at
the time it was added to the registry. The description does not
replace the content of the source standard itself. The descriptions
are not intended to be the localized English names for the subtags.
Localization or translation of language tag and subtag descriptions
is out of scope of this document.
Descriptions SHOULD contain all and only that information necessary
to distinguish one subtag from others that it might be confused with.
They are not intended to provide general background information, nor
to provide all possible alternate names or designations.
3.1.5. Deprecated Field
The field 'Deprecated' MAY be added, changed, or removed from any
record via the maintenance process described in Section 3.3 or via
the registration process described in Section 3.5. Usually, the
addition of a 'Deprecated' field is due to the action of one of the
standards bodies, such as ISO 3166, withdrawing a code. Although
valid in language tags, subtags and tags with a 'Deprecated' field
are deprecated and validating processors SHOULD NOT generate these
subtags. Note that a record that contains a 'Deprecated' field and
no corresponding 'Preferred-Value' field has no replacement mapping.
In some historical cases, it might not have been possible to
reconstruct the original deprecation date. For these cases, an
approximate date appears in the registry. Some subtags and some
grandfathered or redundant tags were deprecated before the initial
creation of the registry. The exact rules for this appear in Section
2 of [RFC4645]. Note that these records have a 'Deprecated' field
with an earlier date then the corresponding 'Added' field!
3.1.6. Preferred-Value Field
The field 'Preferred-Value' contains a mapping between the record in
which it appears and another tag or subtag. The value in this field
is strongly RECOMMENDED as the best choice to represent the value of
this record when selecting a language tag. These values form three
groups:
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1. ISO 639 language codes that were later withdrawn in favor of
other codes. These values are mostly a historical curiosity.
2. Codes that have been withdrawn in favor of a new code. In
particular, this applies to region subtags taken from ISO 3166-1,
because sometimes a country will change its name or
administration in such a way that warrants a new region code. In
some cases, countries have reverted to an older name, which might
already be encoded.
3. Tags or subtags that have become obsolete because the values they
represent were later encoded. Many of the grandfathered or
redundant tags were later encoded by ISO 639, for example, and
fit this pattern.
Records that contain a 'Preferred-Value' field MUST also have a
'Deprecated' field. This field contains the date on which the tag or
subtag was deprecated in favor of the preferred value.
Note that 'Preferred-Value' mappings in records of type 'region'
sometimes do not represent exactly the same meaning as the original
value. There are many reasons for a country code to be changed, and
the effect this has on the formation of language tags will depend on
the nature of the change in question.
A 'Preferred-Value' MAY be added to, changed, or removed from records
according to the rules in Section 3.3. Addition, modification, or
removal of a 'Preferred-Value' field in a record does not imply that
content using the affected subtag needs to be retagged.
The 'Preferred-Value' field in records of type "grandfathered" and
"redundant" contains whole language tags that are strongly
RECOMMENDED for use in place of the record's value. In many cases,
these mappings were created via deprecation of the tags during the
period before [RFC4646] was adopted. For example, the tag "no-nyn"
was deprecated in favor of the ISO 639-1-defined language code 'nn'.
Usually the addition, removal, or change of a Preferred-Value field
for a subtag is done to reflect changes in one of the source
standards. For example, if an ISO 3166-1 region code is deprecated
in favor of another code, that SHOULD result in the addition of a
Preferred-Value field.
Changes to one subtag MAY affect other subtags as well: when
proposing changes to the registry, the Language Subtag Reviewer will
review the registry for such effects and propose the necessary
changes using the process in Section 3.5, although anyone MAY request
such changes. For example:
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Suppose that subtag 'XX' has a Preferred-Value of 'YY'. If 'YY'
later changes to have a Preferred-Value of 'ZZ', then the
Preferred-Value for 'XX' MUST also change to be 'ZZ'.
Suppose that a registered language subtag 'dialect' represents a
language not yet available in any part of ISO 639. The later
addition of a corresponding language code in ISO 639 SHOULD result
in the addition of a Preferred-Value for 'dialect'.
3.1.7. Prefix Field
The 'Prefix' field contains an extended language range whose subtags
are appropriate to use with this subtag: each of the subtags in one
of the subtag's Prefix fields SHOULD appear before the variant in a
valid tag. For example, the variant subtag '1996' has a 'Prefix'
field of "de". This means that tags starting with the sequence "de-"
are appropriate with this subtag, so "de-Latg-1996" and "de-CH-1996"
are both acceptable, while the tag "fr-1996" is an inappropriate
choice.
The field of type 'Prefix' MUST NOT be removed from any record. The
field-body for this type of field MAY be modified, but only if the
modification broadens the meaning of the subtag. That is, the field-
body can be replaced only by a prefix of itself. For example, the
Prefix "be-Latn" (Belarusian, Latin script) could be replaced by the
Prefix "be" (Belarusian) but not by the Prefix "ru-Latn" (Russian,
Latin script).
Records of type 'variant' MAY have more than one field of type
'Prefix'. Additional fields of this type MAY be added to a 'variant'
record via the registration process.
The field-body of the 'Prefix' field MUST NOT conflict with any
'Prefix' already registered for a given record. Such a conflict
would occur when no valid tag could be constructed that would contain
the prefix, such as when two subtags each have a 'Prefix' that
contains the other subtag. For example, suppose that the subtag
'avariant' has the prefix "es-bvariant". Then the subtag 'bvariant'
cannot given the prefix 'avariant', for that would require a tag of
the form "es-avariant-bvariant-avariant", which would not be valid.
3.1.8. Suppress-Script Field
The field 'Suppress-Script' contains a script subtag (whose record
appears in the registry). The field 'Suppress-Script' MUST only
appear in records whose 'Type' field-body is 'language'. This field
MUST NOT appear more than one time in a record. This field indicates
a script used to write the overwhelming majority of documents for the
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given language. This script code therefore adds no distinguishing
information to a language tag. This helps ensure greater
compatibility between the language tags generated according to the
rules in this document and language tags and tag processors or
consumers based on RFC 3066 by indicating that the script subtag
SHOULD NOT be used for most documents in that language. For example,
virtually all Icelandic documents are written in the Latin script,
making the subtag 'Latn' redundant in the tag "is-Latn".
Many language subtag records do not have a Suppress-Script field.
The lack of a Suppress-Script might indicate that the language is
customarily written in more than one script or that the language is
not customarily written at all. It might also mean that sufficient
information was not available when the record was created and thus
remains a candidate for future registration.
3.1.9. Macrolanguage Field
The field 'Macrolanguage' contains a primary language subtag (whose
record appears in the registry). This field indicates a language
that encompasses this subtag's language according to assignments made
by ISO 639-3.
ISO 639-3 labels some languages in the registry as "macrolanguages".
ISO 639-3 defines the term "Macrolanguage" to mean "clusters of
closely-related language varieties that [...] can be considered
distinct individual languages, yet in certain usage contexts a single
language identity for all is needed". These correspond to codes
registered in ISO 639-2 as individual languages that were found to
correspond to more than one language in ISO 639-3.
A language contained within a macrolanguage is called an "encompassed
language". The record for each encompassed language contains a
'Macrolanguage' field in the registry; the macrolanguages themselves
are not specially marked. Note that some encompassed languages have
ISO 639-1 or ISO 639-2 codes.
The Macrolanguage field can only occur in records of type 'language'.
Only values assigned by ISO 639-3 will be considered for inclusion.
Macrolanguage fields MAY be added or removed via the normal
registration process whenever ISO 639-3 defines new values or
withdraws old values. Macrolanguages are informational, and MAY be
removed or changed if ISO 639-3 changes the values. For more
information on the use of this field and choosing between
macrolanguage and encompassed language subtags, see Section 4.1.1.
For example, the language subtags 'nb' (Norwegian Bokmal) and 'nn'
(Norwegian Nynorsk) each have a Macrolanguage entry of 'no'
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(Norwegian). For more information see Section 4.1.
3.1.10. Comments Field
The field 'Comments' conveys additional information about the record
and MAY appear more than once per record. The field-body MAY include
the full range of Unicode characters and is not restricted to any
particular script. This field MAY be inserted or changed via the
registration process and no guarantee of stability is provided.
The content of this field is not restricted, except by the need to
register the information, the suitability of the request, and by
reasonable practical size limitations. The primary reason for the
Comments field is subtag identification: to help distinguish the
subtag from others with which it might be confused. In particular,
large amounts of information about the use, history, or general
background of a subtag are frowned upon as these generally belong and
are encouraged in registration request forms themselves, but do not
belong in the registry record proper.
3.2. Language Subtag Reviewer
The Language Subtag Reviewer moderates the ietf-languages mailing
list, responds to requests for registration, and performs the other
registry maintenance duties described in Section 3.3. Only the
Language Subtag Reviewer is permitted to request IANA to change,
update, or add records to the Language Subtag Registry. The Language
Subtag Reviewer MAY delegate list moderation and other clerical
duties as needed.
The Language Subtag Reviewer is appointed by the IESG for an
indefinite term, subject to removal or replacement at the IESG's
discretion. The IESG will solicit nominees for the position (upon
adoption of this document or upon a vacancy) and then solicit
feedback on the nominees' qualifications. Qualified candidates
should be familiar with BCP 47 and its requirements; be willing to
fairly, responsively, and judiciously administer the registration
process; and be suitably informed about the issues of language
identification so that the reviewer can assess the claims and draw
upon the contributions of language experts and subtag requesters.
The subsequent performance or decisions of the Language Subtag
Reviewer MAY be appealed to the IESG under the same rules as other
IETF decisions (see [RFC2026]). The IESG can reverse or overturn the
decisions of the Language Subtag Reviewer, provide guidance, or take
other appropriate actions.
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3.3. Maintenance of the Registry
Maintenance of the registry requires that as codes are assigned or
withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language
Subtag Reviewer MUST evaluate each change and determine the
appropriate course of action according to the rules in this document.
Such updates follow the registration process described in
Section 3.5. Usually the Language Subtag Reviewer will start the
process for the new or updated record by filling in the registration
form and submitting it. If a change to one of these standards takes
place and the Language Subtag Reviewer does not do this in a timely
manner, then any interested party MAY submit the form. Thereafter
the registration process continues normally.
Note that some registrations affect other subtags--perhaps more than
one--as when a region subtag is being deprecated in favor of a new
value. The Language Subtag Reviewer is responsible for ensuring that
any such changes are properly registered, with each change requiring
its own registration form.
The Language Subtag Reviewer MUST ensure that new subtags meet the
requirements elsewhere in this document (and most especially in
Section 3.4) or submit an appropriate registration form for an
alternate subtag as described in that section. Each individual
subtag affected by a change MUST be sent to the ietf-languages list
with its own registration form and in a separate message.
3.4. Stability of IANA Registry Entries
The stability of entries and their meaning in the registry is
critical to the long-term stability of language tags. The rules in
this section guarantee that a specific language tag's meaning is
stable over time and will not change.
These rules specifically deal with how changes to codes (including
withdrawal and deprecation of codes) maintained by ISO 639, ISO
15924, ISO 3166, and UN M.49 are reflected in the IANA Language
Subtag Registry. Assignments to the IANA Language Subtag Registry
MUST follow the following stability rules:
1. Values in the fields 'Type', 'Subtag', 'Tag', and 'Added' MUST
NOT be changed and are guaranteed to be stable over time.
2. Values in the fields 'Preferred-Value' and 'Deprecated' MAY be
added, altered, or removed via the registration process. These
changes SHOULD be limited to changes necessary to mirror changes
in one of the underlying standards (ISO 639, ISO 15924, ISO
3166-1, or UN M.49) and typically alteration or removal of a
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Preferred-Value is limited specifically to region codes.
3. Values in the 'Description' field MUST NOT be changed in a way
that would invalidate previously-existing tags. They MAY be
broadened somewhat in scope, changed to add information, or
adapted to the most common modern usage. For example, countries
occasionally change their names; a historical example of this
would be "Upper Volta" changing to "Burkina Faso".
4. Values in the field 'Prefix' MAY be added to records of type
'variant' via the registration process. If a prefix is added to
a variant record, 'Comment' fields SHOULD be used to explain
different usages with the various prefixes.
5. Values in the field 'Prefix' in records of type 'variant' MAY be
modified, so long as the modifications broaden the set of
prefixes. That is, a prefix MAY be replaced by one of its own
prefixes. For example, the prefix "en-US" could be replaced by
"en", but not by the prefixes "en-Latn", "fr", or "en-US-boont".
If one of those prefixes were needed, a new Prefix SHOULD be
registered.
6. Values in the field 'Prefix' MUST NOT be removed.
7. The field 'Comments' MAY be added, changed, modified, or removed
via the registration process or any of the processes or
considerations described in this section.
8. The field 'Suppress-Script' MAY be added or removed via the
registration process.
9. The field 'Macrolanguage' MAY be added or removed via the
registration process, but only in response to changes made by
ISO 639. The Macrolanguage field appears whenever a language
has a corresponding Macrolanguage in ISO 639. That is, the
macrolanguage fields in the registry exactly match those of ISO
639. No other macrolanguage mappings will be considered for
registration.
10. Codes assigned by ISO 639-1 that do not conflict with existing
two-letter primary language subtags and which have no
corresponding three-letter primary defined in the registry are
entered into the IANA registry as new records of type
'language'.
11. Codes assigned by ISO 639-2 that do not conflict with existing
three-letter primary language subtags are entered into the IANA
registry as new records of type 'language'.
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12. Codes assigned by ISO 639-3 that do not conflict with existing
three-letter primary language subtags are entered into the IANA
registry as new primary language records.
13. Codes assigned by ISO 15924 and ISO 3166-1 that do not conflict
with existing subtags of the associated type and whose meaning
is not the same as an existing subtag of the same type are
entered into the IANA registry as new records.
14. Codes assigned by ISO 639, ISO 15924, or ISO 3166-1 that are
withdrawn by their respective maintenance or registration
authority remain valid in language tags. A 'Deprecated' field
containing the date of withdrawal MUST be added to the record.
If a new record of the same type is added that represents a
replacement value, then a 'Preferred-Value' field MAY also be
added. The registration process MAY be used to add comments
about the withdrawal of the code by the respective standard.
Example The region code 'TL' was assigned to the country
'Timor-Leste', replacing the code 'TP' (which was assigned to
'East Timor' when it was under administration by Portugal).
The subtag 'TP' remains valid in language tags, but its
record contains the a 'Preferred-Value' of 'TL' and its field
'Deprecated' contains the date the new code was assigned
('2004-07-06').
15. Codes assigned by ISO 639, ISO 15924, or ISO 3166-1 that
conflict with existing subtags of the associated type, including
subtags that are deprecated, MUST NOT be entered into the
registry. The following additional considerations apply to
subtag values that are reassigned:
A. For ISO 639 codes, if the newly assigned code's meaning is
not represented by a subtag in the IANA registry, the
Language Subtag Reviewer, as described in Section 3.5, SHALL
prepare a proposal for entering in the IANA registry as soon
as practical a registered language subtag as an alternate
value for the new code. The form of the registered language
subtag will be at the discretion of the Language Subtag
Reviewer and MUST conform to other restrictions on language
subtags in this document.
B. For all subtags whose meaning is derived from an external
standard (that is, by ISO 639, ISO 15924, ISO 3166-1, or UN
M.49), if a new meaning is assigned to an existing code and
the new meaning broadens the meaning of that code, then the
meaning for the associated subtag MAY be changed to match.
The meaning of a subtag MUST NOT be narrowed, however, as
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this can result in an unknown proportion of the existing
uses of a subtag becoming invalid. Note: ISO 639
registration authority (RA) has adopted a similar stability
policy.
C. For ISO 15924 codes, if the newly assigned code's meaning is
not represented by a subtag in the IANA registry, the
Language Subtag Reviewer, as described in Section 3.5, SHALL
prepare a proposal for entering in the IANA registry as soon
as practical a registered variant subtag as an alternate
value for the new code. The form of the registered variant
subtag will be at the discretion of the Language Subtag
Reviewer and MUST conform to other restrictions on variant
subtags in this document.
D. For ISO 3166-1 codes, if the newly assigned code's meaning
is associated with the same UN M.49 code as another 'region'
subtag, then the existing region subtag remains as the
preferred value for that region and no new entry is created.
A comment MAY be added to the existing region subtag
indicating the relationship to the new ISO 3166-1 code.
E. For ISO 3166-1 codes, if the newly assigned code's meaning
is associated with a UN M.49 code that is not represented by
an existing region subtag, then the Language Subtag
Reviewer, as described in Section 3.5, SHALL prepare a
proposal for entering the appropriate UN M.49 country code
as an entry in the IANA registry.
F. For ISO 3166-1 codes, if there is no associated UN numeric
code, then the Language Subtag Reviewer SHALL petition the
UN to create one. If there is no response from the UN
within ninety days of the request being sent, the Language
Subtag Reviewer SHALL prepare a proposal for entering in the
IANA registry as soon as practical a registered variant
subtag as an alternate value for the new code. The form of
the registered variant subtag will be at the discretion of
the Language Subtag Reviewer and MUST conform to other
restrictions on variant subtags in this document. This
situation is very unlikely to ever occur.
16. UN M.49 has codes for both countries and areas (such as '276'
for Germany) and geographical regions and sub-regions (such as
'150' for Europe). UN M.49 country or area codes for which
there is no corresponding ISO 3166-1 code SHOULD NOT be
registered, except as a surrogate for an ISO 3166-1 code that is
blocked from registration by an existing subtag. If such a code
becomes necessary, then the registration authority for ISO
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3166-1 SHOULD first be petitioned to assign a code to the
region. If the petition for a code assignment by ISO 3166-1 is
refused or not acted on in a timely manner, the registration
process described in Section 3.5 MAY then be used to register
the corresponding UN M.49 code. This way, UN M.49 codes remain
available as the value of last resort in cases where ISO 3166-1
reassigns a deprecated value in the registry.
17. Stability provisions apply to grandfathered tags with this
exception: should it become possible to compose one of the
grandfathered tags from registered subtags, then the field
'Type' in that record is changed from 'grandfathered' to
'redundant'. Note that this will not affect language tags that
match the grandfathered tag, since these tags will now match
valid generative subtag sequences. For example, the variant
subtag '1901' is registered, making the formerly-grandfathered
tags such as "de-1901" and "de-AT-1901" redundant as a result.
Of course, these tags, where applied to existing content or in
existing implementations, remain valid (all of their subtags are
in the registry, after all), while new tags or applications
using these subtags become possible.
Note: The redundant and grandfathered entries together are the
complete list of tags registered under [RFC3066]. The redundant tags
are those that can now be formed using the subtags defined in the
registry together with the rules of Section 2.2. The grandfathered
entries include those that can never be legal under those same
provisions plus those tags that contain subtags not yet registered
or, perhaps, inappropriate for registration.
The set of redundant and grandfathered tags is permanent and stable:
new entries in this section MUST NOT be added and existing entries
MUST NOT be removed. Records of type 'grandfathered' MAY have their
type converted to 'redundant'; see item 12 in Section 3.6 for more
information. The decision-making process about which tags were
initially grandfathered and which were made redundant is described in
[RFC4645].
RFC 3066 tags that were deprecated prior to the adoption of [RFC4646]
are part of the list of grandfathered tags, and their component
subtags were not included as registered variants (although they
remain eligible for registration). For example, the tag "art-lojban"
was deprecated in favor of the language subtag 'jbo'.
3.5. Registration Procedure for Subtags
The procedure given here MUST be used by anyone who wants to use a
subtag not currently in the IANA Language Subtag Registry.
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Only subtags of type 'language' and 'variant' will be considered for
independent registration of new subtags. Subtags needed for
stability and subtags necessary to keep the registry synchronized
with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits
defined by this document also use this process, as described in
Section 3.3. Stability provisions are described in Section 3.4.
This procedure MAY also be used to register or alter the information
for the 'Comments', 'Deprecated', 'Description', 'Prefix',
'Preferred-Value', or 'Suppress-Script' fields in a subtag's record
as described in Section 3.4. Changes to all other fields in the IANA
registry are NOT permitted.
Registering a new subtag or requesting modifications to an existing
tag or subtag starts with the requester filling out the registration
form reproduced below. Note that each response is not limited in
size so that the request can adequately describe the registration.
The fields in the "Record Requested" section SHOULD follow the
requirements in Section 3.1.
LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester:
2. E-mail address of requester:
3. Record Requested:
Type:
Subtag:
Description:
Prefix:
Preferred-Value:
Deprecated:
Suppress-Script:
Macrolanguage:
Comments:
4. Intended meaning of the subtag:
5. Reference to published description
of the language (book or article):
6. Any other relevant information:
Figure 6: The Language Subtag Registration Form
Examples of completed registration forms can be found in Appendix C
or online at http://www.iana.org/assignments/lang-subtags-templates/.
The subtag registration form MUST be sent to
<ietf-languages@iana.org> for a two-week review period before it can
be submitted to IANA. If modifications are made to the request
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during the course of the registration process (such as corrections to
meet the requirements in Section 3.1) the modified form MUST also be
sent to <ietf-languages@iana.org> at least one week prior to
submission to IANA.
The ietf-languages list is an open list and can be joined by sending
a request to <ietf-languages-request@iana.org>. The list can be
hosted by IANA or by any third party at the request of IESG.
Before forwarding a new registration to IANA, the Language Subtag
Reviewer MUST ensure that all requirements in this document are met
and that values in the 'Subtag' field match case according to the
description in Section 3.1. The Reviewer MUST also ensure that an
appropriate File-Date record is included in the request, to assist
IANA when updating the registry (see Section 5.1).
Some fields in both the registration form as well as the registry
record itself permit the use of non-ASCII characters. Registration
requests SHOULD use the UTF-8 encoding for consistency and clarity.
However, since some mail clients do not support this encoding, other
encodings MAY be used for the registration request. The Language
Subtag Reviewer is responsible for ensuring that the proper Unicode
characters appear in both the archived request form and the registry
record. In the case of a transcription or encoding error by IANA,
the Language Subtag Reviewer will request that the registry be
repaired, providing any necessary information to assist IANA.
Variant subtags are usually registered for use with a particular
range of language tags. For example, the subtag 'rozaj' is intended
for use with language tags that start with the primary language
subtag "sl", since Resian is a dialect of Slovenian. Thus, the
subtag 'rozaj' would be appropriate in tags such as "sl-Latn-rozaj"
or "sl-IT-rozaj". This information is stored in the 'Prefix' field
in the registry. Variant registration requests SHOULD include at
least one 'Prefix' field in the registration form.
The 'Prefix' field for a given registered subtag exists in the IANA
registry as a guide to usage. Additional prefixes MAY be added by
filing an additional registration form. In that form, the "Any other
relevant information:" field MUST indicate that it is the addition of
a prefix.
Requests to add a prefix to a variant subtag that imply a different
semantic meaning SHOULD be rejected. For example, a request to add
the prefix "de" to the subtag 'nedis' so that the tag "de-nedis"
represented some German dialect would be rejected. The 'nedis'
subtag represents a particular Slovenian dialect and the additional
registration would change the semantic meaning assigned to the
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subtag. A separate subtag SHOULD be proposed instead.
The 'Description' field MUST contain a description of the tag being
registered written or transcribed into the Latin script; it MAY also
include a description in a non-Latin script. The 'Description' field
is used for identification purposes and doesn't necessarily represent
the actual native name of the language or variation or to be in any
particular language.
While the 'Description' field itself is not guaranteed to be stable
and errata corrections MAY be undertaken from time to time, attempts
to provide translations or transcriptions of entries in the registry
itself will probably be frowned upon by the community or rejected
outright, as changes of this nature have an impact on the provisions
in Section 3.4.
When the two-week period has passed, the Language Subtag Reviewer
MUST take one of the following actions:
o Explicitly accept the request and forward the form containing the
record to be inserted or modified to iana@iana.org according to
the procedure described in Section 3.3.
o Explicitly reject the request because of significant objections
raised on the list or due to problems with constraints in this
document (which MUST be explicitly cited).
o Extend the review period by granting an additional two-week
increment to permit further discussion. After each two-week
increment, the Language Subtag Reviewer MUST indicate on the list
whether the registration has been accepted, rejected, or extended.
Note that the Language Subtag Reviewer MAY raise objections on the
list if he or she so desires. The important thing is that the
objection MUST be made publicly.
Sometimes the request needs to be modified as a result of discussion
during the review period or due to requirements in this document.
The applicant, Language Subtag Reviewer, or others are free to submit
a modified version of the completed registration form, which will be
considered in lieu of the original request with the explicit approval
of the applicant. Such changes do not restart the two-week
discussion period, although an application containing the final
record submitted to IANA MUST appear on the list at least one week
prior to the Language Subtag Reviewer forwarding the record to IANA.
The applicant is also free to modify a rejected application with
additional information and submit it again; this starts a new two-
week comment period.
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Registrations initiated due to the provisions of Section 3.3 or
Section 3.4 SHALL NOT be rejected altogether (since they have to
ultimately appear in the registry) and SHOULD be completed as quickly
as possible. The review process allows list members to comment on
the specific information in the form and the record it contains and
thus help ensure that it is correct and consistent. The Language
Subtag Reviewer MAY reject a specific version of the form, but MUST
include in the rejection a suitable replacement, extending the review
period as described above, until the form is in a format worthy of
reviewer's approval.
Decisions made by the Language Subtag Reviewer MAY be appealed to the
IESG [RFC2028] under the same rules as other IETF decisions
[RFC2026]. This includes a decision to extend the review period or
the failure to announce a decision in a clear and timely manner.
The approved records appear in the Language Subtag Registry. The
approved registration forms are available online under
http://www.iana.org/assignments/lang-subtags-templates/.
Updates or changes to existing records follow the same procedure as
new registrations. The Language Subtag Reviewer decides whether
there is consensus to update the registration following the two week
review period; normally, objections by the original registrant will
carry extra weight in forming such a consensus.
Registrations are permanent and stable. Once registered, subtags
will not be removed from the registry and will remain a valid way in
which to specify a specific language or variant.
Note: The purpose of the "Reference to published description" section
in the registration form is to aid in verifying whether a language is
registered or what language or language variation a particular subtag
refers to. In most cases, reference to an authoritative grammar or
dictionary of that language will be useful; in cases where no such
work exists, other well-known works describing that language or in
that language MAY be appropriate. The Language Subtag Reviewer
decides what constitutes "good enough" reference material. This
requirement is not intended to exclude particular languages or
dialects due to the size of the speaker population or lack of a
standardized orthography. Minority languages will be considered
equally on their own merits.
3.6. Possibilities for Registration
Possibilities for registration of subtags or information about
subtags include:
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o Primary language subtags for languages not listed in ISO 639 that
are not variants of any listed or registered language MAY be
registered. At the time this document was created, there were no
examples of this form of subtag. Before attempting to register a
language subtag, there MUST be an attempt to register the language
with ISO 639. Subtags MUST NOT be registered for languages
defined by codes that exist in ISO 639-1, ISO 639-2, or ISO 639-3,
or that are under consideration by the ISO 639 registration
authorities, or that have never been attempted for registration
with those authorities. If ISO 639 has previously rejected a
language for registration, it is reasonable to assume that there
must be additional, very compelling evidence of need before it
will be registered as a primary language subtag in the IANA
registry (to the extent that it is very unlikely that any subtags
will be registered of this type).
o Dialect or other divisions or variations within a language, its
orthography, writing system, regional or historical usage,
transliteration or other transformation, or distinguishing
variation MAY be registered as variant subtags. An example is the
'rozaj' subtag (the Resian dialect of Slovenian).
o The addition or maintenance of fields (generally of an
informational nature) in Tag or Subtag records as described in
Section 3.1 and subject to the stability provisions in
Section 3.4. This includes descriptions, comments, deprecation
and preferred values for obsolete or withdrawn codes, or the
addition of script or macrolanguage information to primary
language subtags.
o The addition of records and related field value changes necessary
to reflect assignments made by ISO 639, ISO 15924, ISO 3166-1, and
UN M.49 as described in Section 3.4.
Subtags proposed for registration that would cause all or part of a
grandfathered tag to become redundant but whose meaning conflicts
with or alters the meaning of the grandfathered tag MUST be rejected.
This document leaves the decision on what subtags or changes to
subtags are appropriate (or not) to the registration process
described in Section 3.5.
Note: four-character primary language subtags are reserved to allow
for the possibility of alpha4 codes in some future addition to the
ISO 639 family of standards.
ISO 639 defines a for additions to and changes in the list of
languages in ISO 639. This agency is:
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International Information Centre for Terminology (Infoterm)
Aichholzgasse 6/12, AT-1120
Wien, Austria
Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72
ISO 639-2 defines a registration authority for additions to and
changes in the list of languages in ISO 639-2. This agency is:
Library of Congress
Network Development and MARC Standards Office
Washington, D.C. 20540 USA
Phone: +1 202 707 6237 Fax: +1 202 707 0115
URL: http://www.loc.gov/standards/iso639-2
ISO 639-3 defines a registration authority for additions to and
changes in the list of languages in ISO 639-3. This agency is:
SIL International
ISO 639-3 Registrar
7500 W. Camp Wisdom Rd.
Dallas, TX 75236 USA
Phone: +1 972 708 7400, ext. 2293 Fax: +1 972 708 7546
Email: iso639-3@sil.org
URL: http://www.sil.org/iso639-3
The maintenance agency for ISO 3166-1 (country codes) is:
ISO 3166 Maintenance Agency
c/o International Organization for Standardization
Case postale 56
CH-1211 Geneva 20 Switzerland
Phone: +41 22 749 72 33 Fax: +41 22 749 73 49
URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html
The registration authority for ISO 15924 (script codes) is:
Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
URL: http://www.unicode.org/iso15924
The Statistics Division of the United Nations Secretariat maintains
the Standard Country or Area Codes for Statistical Use and can be
reached at:
Statistical Services Branch
Statistics Division
United Nations, Room DC2-1620
New York, NY 10017, USA
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Fax: +1-212-963-0623
E-mail: statistics@un.org
URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm
3.7. Extensions and the Extensions Registry
Extension subtags are those introduced by single-character subtags
("singletons") other than 'x'. They are reserved for the generation
of identifiers that contain a language component and are compatible
with applications that understand language tags.
The structure and form of extensions are defined by this document so
that implementations can be created that are forward compatible with
applications that might be created using singletons in the future.
In addition, defining a mechanism for maintaining singletons will
lend stability to this document by reducing the likely need for
future revisions or updates.
Single-character subtags are assigned by IANA using the "IETF
Consensus" policy defined by [RFC2434]. This policy requires the
development of an RFC, which SHALL define the name, purpose,
processes, and procedures for maintaining the subtags. The
maintaining or registering authority, including name, contact email,
discussion list email, and URL location of the registry, MUST be
indicated clearly in the RFC. The RFC MUST specify or include each
of the following:
o The specification MUST reference the specific version or revision
of this document that governs its creation and MUST reference this
section of this document.
o The specification and all subtags defined by the specification
MUST follow the ABNF and other rules for the formation of tags and
subtags as defined in this document. In particular, it MUST
specify that case is not significant and that subtags MUST NOT
exceed eight characters in length.
o The specification MUST specify a canonical representation.
o The specification of valid subtags MUST be available over the
Internet and at no cost.
o The specification MUST be in the public domain or available via a
royalty-free license acceptable to the IETF and specified in the
RFC.
o The specification MUST be versioned, and each version of the
specification MUST be numbered, dated, and stable.
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o The specification MUST be stable. That is, extension subtags,
once defined by a specification, MUST NOT be retracted or change
in meaning in any substantial way.
o The specification MUST include in a separate section the
registration form reproduced in this section (below) to be used in
registering the extension upon publication as an RFC.
o IANA MUST be informed of changes to the contact information and
URL for the specification.
IANA will maintain a registry of allocated single-character
(singleton) subtags. This registry MUST use the record-jar format
described by the ABNF in Section 3.1. Upon publication of an
extension as an RFC, the maintaining authority defined in the RFC
MUST forward this registration form to iesg@ietf.org, who MUST
forward the request to iana@iana.org. The maintaining authority of
the extension MUST maintain the accuracy of the record by sending an
updated full copy of the record to iana@iana.org with the subject
line "LANGUAGE TAG EXTENSION UPDATE" whenever content changes. Only
the 'Comments', 'Contact_Email', 'Mailing_List', and 'URL' fields MAY
be modified in these updates.
Failure to maintain this record, maintain the corresponding registry,
or meet other conditions imposed by this section of this document MAY
be appealed to the IESG [RFC2028] under the same rules as other IETF
decisions (see [RFC2026]) and MAY result in the authority to maintain
the extension being withdrawn or reassigned by the IESG.
%%
Identifier:
Description:
Comments:
Added:
RFC:
Authority:
Contact_Email:
Mailing_List:
URL:
%%
Figure 7: Format of Records in the Language Tag Extensions Registry
'Identifier' contains the single-character subtag (singleton)
assigned to the extension. The Internet-Draft submitted to define
the extension SHOULD specify which letter or digit to use, although
the IESG MAY change the assignment when approving the RFC.
'Description' contains the name and description of the extension.
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'Comments' is an OPTIONAL field and MAY contain a broader description
of the extension.
'Added' contains the date the extension's RFC was published in the
"full-date" format specified in [RFC3339]. For example: 2004-06-28
represents June 28, 2004, in the Gregorian calendar.
'RFC' contains the RFC number assigned to the extension.
'Authority' contains the name of the maintaining authority for the
extension.
'Contact_Email' contains the email address used to contact the
maintaining authority.
'Mailing_List' contains the URL or subscription email address of the
mailing list used by the maintaining authority.
'URL' contains the URL of the registry for this extension.
The determination of whether an Internet-Draft meets the above
conditions and the decision to grant or withhold such authority rests
solely with the IESG and is subject to the normal review and appeals
process associated with the RFC process.
Extension authors are strongly cautioned that many (including most
well-formed) processors will be unaware of any special relationships
or meaning inherent in the order of extension subtags. Extension
authors SHOULD avoid subtag relationships or canonicalization
mechanisms that interfere with matching or with length restrictions
that sometimes exist in common protocols where the extension is used.
In particular, applications MAY truncate the subtags in doing
matching or in fitting into limited lengths, so it is RECOMMENDED
that the most significant information be in the most significant
(left-most) subtags and that the specification gracefully handle
truncated subtags.
When a language tag is to be used in a specific, known, protocol, it
is RECOMMENDED that the language tag not contain extensions not
supported by that protocol. In addition, note that some protocols
MAY impose upper limits on the length of the strings used to store or
transport the language tag.
3.8. Update of the Language Subtag Registry
Upon adoption of this document the IANA Language Subtag Registry will
need an update so that it contains the complete set of subtags valid
in a language tag. This collection of subtags, along with a
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description of the process used to create it, is described by
[registry-update]. IANA will publish the updated version of the
registry described by this document using the instructions and
content of [registry-update]. Once published by IANA, the
maintenance procedures, rules, and registration processes described
in this document will be available for new registrations or updates.
Registrations that are in process under the rules defined in
[RFC4646] when this document is adopted MUST be completed under the
rules contained in this document.
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4. Formation and Processing of Language Tags
This section addresses how to use the information in the registry
with the tag syntax to choose, form, and process language tags.
4.1. Choice of Language Tag
The guiding principle in forming language tags is to "tag content
wisely." Sometimes there is a choice between several possible tags
for the same content. The choice of which tag to use depends on the
content and application in question and some amount of judgment might
be necessary when selecting a tag.
Interoperability is best served when the same language tag is used
consistently to represent the same language. If an application has
requirements that make the rules here inapplicable, then that
application risks damaging interoperability. It is strongly
RECOMMENDED that users not define their own rules for language tag
choice.
Standards, protocols, and applications that reference this document
normatively but apply different rules to the ones given in this
section MUST specify how language tag selection varies from the
guidelines given here.
To ensure consistent backward compatibility, this document contains
several provisions to account for potential instability in the
standards used to define the subtags that make up language tags.
These provisions mean that no valid language tag can become invalid,
nor will a language tag have a narrower scope in the future (it may
have a broader scope). The most appropriate language tag for a given
application or content item might evolve over time, but once tagged
the content cannot become invalid.
A subtag SHOULD only be used when it adds useful distinguishing
information to the tag. Extraneous subtags interfere with the
meaning, understanding, and processing of language tags. In
particular, users and implementations SHOULD follow the 'Prefix' and
'Suppress-Script' fields in the registry (defined in Section 3.1):
these fields provide guidance on when specific additional subtags
SHOULD be used or avoided in a language tag.
Some applications can benefit from the use of script subtags in
language tags, as long as the use is consistent for a given context.
Script subtags are never appropriate for unwritten content (such as
audio recordings).
Script subtags were formally defined in BCP 47 by [RFC4646]. Their
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use can affect matching and subtag identification for implementations
of previous versions of BCP 47 (i.e. [RFC1766] or [RFC3066]), as
these subtags appear between the primary language and region subtags.
For example, if an implementation selects content using Basic
Filtering [RFC4647] (originally described in Section 2.5 of
[RFC3066]) and the user requested the language range "en-US", content
labeled "en-Latn-US" will not match the request and thus not be
selected. Therefore, it is important to know when script subtags
will customarily be used and when they ought not be used. In the
registry, the Suppress-Script field helps ensure greater
compatibility between the language tags by defining when users SHOULD
NOT include a script subtag with a particular primary language
subtag.
The choice of subtags used to form a language tag SHOULD follow these
guidelines:
1. Use as precise a tag as possible, but no more specific than is
justified. Avoid using subtags that are not important for
distinguishing content in an application.
* For example, 'de' might suffice for tagging an email written
in German, while "de-CH-1996" is probably unnecessarily
precise for such a task.
* Note that some subtag sequences might not represent the
language a casual user might expect, especially if when
relying on the subtag's description in the registry. For
example, the Swiss German (Schweizerdeutsch) language is
represented by "gsw-CH" and not by "de-CH". This latter tag
represents German ('de') as used in Switzerland ('CH'), also
known as Swiss High German (Schweizer Hochdeutsch). Both are
real languages and distinguishing between them could be
important to an application.
2. The script subtag SHOULD NOT be used to form language tags unless
the script adds some distinguishing information to the tag. The
field 'Suppress-Script' in the primary language record in the
registry indicates script subtags that do not add distinguishing
information for most applications. For example:
* The subtag 'Latn' should not be used with the primary language
'en' because nearly all English documents are written in the
Latin script and it adds no distinguishing information.
However, if a document were written in English mixing Latin
script with another script such as Braille ('Brai'), then it
might be appropriate to choose to indicate both scripts to aid
in content selection, such as the application of a style
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sheet.
* When labeling content that is unwritten (such as a recording
of human speech), the script subtag should not be used, even
if the language is customarily written in several scripts.
Thus the subtitles to a movie might use the tag "uz-Arab"
(Uzbek, Arabic script), but the audio track for the same
language would be tagged simply "uz". (The tag "uz-Zxxx"
could also be used where content is not written, as the subtag
'Zxxx' represents the "Code for unwritten documents".)
3. If a tag or subtag has a 'Preferred-Value' field in its registry
entry, then the value of that field SHOULD be used to form the
language tag in preference to the tag or subtag in which the
preferred value appears.
* For example, use 'he' for Hebrew in preference to 'iw'.
4. [ISO639-2] has defined several codes included in the subtag
registry that require additional care when choosing language
tags. In most of these cases, where omitting the language tag is
permitted, such omission is preferable to using these codes.
Language tags SHOULD NOT incorporate these subtags as a prefix,
unless the additional information conveys some value to the
application.
1. Use specific language subtags or subtag sequences in
preference to subtags for language collections. A "language
collection" is a subtag derived from one of the [ISO639-2]
codes that represents multiple related languages. These
codes are included as primary language subtags in the
registry. For example, the code 'cmc' represents "Chamic
languages". The registry contains values for each of the
approximately ten individual languages represented by this
collective code. Some other examples include the subtags
Germanic languages ('gem') or Algonquian languages ('alg').
Since these codes are interpreted inclusively, content tagged
with "en" (English), "de" (German), or "gsw" (Swiss German,
Alemannic) could also (but SHOULD NOT) be tagged with "gem"
(Germanic languages). Subtags derived from collection codes
SHOULD NOT be used be used unless more specific language
information is not available. Note that matching
implementations generally do not understand the relationship
between the collection and its encompassed languages, and so
users ought not assume a subtag based on a language
collection is a useful means for selecting content in its
encompassed languages.
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2. The 'mul' (Multiple) primary language subtag identifies
content in multiple languages. This subtag SHOULD NOT be
used when a list of languages (such as Content-Language) or
individual tags for each content element can be used instead.
3. The 'und' (Undetermined) primary language subtag identifies
linguistic content whose language is not determined. This
subtag SHOULD NOT be used unless a language tag is required
and language information is not available or cannot be
determined. Omitting the language tag (where permitted) is
preferred. The 'und' subtag MAY be useful for protocols that
require a language tag to be provided or where a primary
language subtag is required (such as in "und-Latn"). The
'und' subtag MAY also be useful when matching language tags
in certain situations.
4. The 'zxx' (Non-Linguistic, Not Applicable) primary language
subtag identifies content for which a language classification
is inappropriate or does not apply. Some examples might
include instrumental or electronic music; sound recordings
consisting of nonverbal sounds; audiovisual materials with no
narration, dialog, printed titles, or subtitles; machine-
readable data files consisting of machine languages or
character codes; or programming source code.
5. The 'mis' (Uncoded) primary language subtag identifies
content whose language is known but which does not currently
have a corresponding subtag. This subtag SHOULD NOT be used.
Because the addition of other codes in the future can render
its application invalid, it is inherently unstable and hence
incompatible with the stability goals of BCP 47. It is
always preferable to use other subtags: either 'und' or (with
prior agreement) private use subtags.
6. The grandfathered tag "i-default" (Default Language) was
originally registered according to [RFC1766] to meet the
needs of [RFC2277]. It is used to indicate not a specific
language, but rather, it identifies the condition or content
used where the language preferences of the user cannot be
established. It SHOULD NOT be used except as a means of
labeling the default content for applications or protocols
that require default language content to be labeled with that
specific tag. It MAY also be used by an application or
protocol to identify when the default language content is
being returned.
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4.1.1. Tagging Encompassed Languages
Some primary language records in the registry have a "Macrolanguage"
field (Section 3.1.9) that contains a mapping from each "encompassed
language" to its macrolanguage. The Macrolanguage mapping doesn't
define what the relationship between the encompassed language and its
macrolanguage is, nor does it define how languages encompassed by the
same macrolanguage are related to each other.　Two different
languages encompassed by the same macrolanguage may differ from one
another more than say, French and Spanish do.
The more specific encompassed language subtag SHOULD be used to form
the language tag, although either the macrolanguage or the
encompassed language subtag MAY be used. This means, for example,
tagging Cantonese ('yue') specifically rather than using the subtag
for its macrolanguage Chinese ('zh'); Tajiki Arabic 'abh' instead of
'ar' (Arabic); Plains Cree with 'crk' rather than 'cre' (Cree); and
so forth.
The family of languages encompassed by the macrolanguage Chinese
('zh') provides a useful illustration of this. Many different kinds
of content have used tags beginning with the 'zh' subtag, with
application specific meaning being associated with region codes in
particular. This is because historically only the macrolanguage
subtag was available for forming language tags. However, these
languages are, in the main, not mutually intelligible when spoken.
Written forms of these languages also show wide variation in form and
usage and many of these languages are written in various contexts.
For some applications, it might be advantageous to use the
macrolanguage subtag to form the tag instead of using the more
specific encompassed language subtag. This is specifically the case
with the Chinese and Arabic language families. For example, an
application with large quantities of textual data already using tags
with the 'zh' (Chinese) subtag might continue to use this more
general subtag even for new data, even though the content could be
more precisely be tagged with 'cmn' (Mandarin). Similarly, an
application already using tags that start with the 'ar' (Arabic)
subtag might continue to use this more general subtag even for new
data, which could be more precisely be tagged with 'arb' (Standard
Arabic).
In some cases, encompassed languages had tags registered for them
during the RFC 3066 era. Those grandfathered tags not already
deprecated were deprecated in the registry upon adoption of this
document. As grandfathered values, they remain valid for use and
some content or applications might use them. As with other
grandfathered tags, since implementations might not be able to
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associate the grandfathered tags with the encompassed language subtag
equivalents that are recommended by this document, implementations
are encouraged to canonicalize tags for comparison purposes. Some
examples of this include the tags "zh-yue" (Cantonese), "zh-hakka"
(Hakka), and "zh-cmn-Hans" (Mandarin Chinese, Simplified Chinese
script).
Each Macrolanguage's subtag, by definition, includes all of its
encompassed languages. Since the relationship between encompassed
languages varies, and, with the exception of a few languages cited in
the table following this paragraph, users cannot assume that the
macrolanguage subtag means any particular encompassed language nor
that any given pair of encompassed languages are mutually
intelligible or otherwise interchangeable. The languages in the
following table represent cases in which the macrolanguage subtag
SHOULD be used in preference to the specified encompassed language
subtag. (The situation regarding Chinese ('zh') and Arabic ('ar') is
discussed above.)
Konkani (macrolanguage) 'kok' Konkani (individual language) 'knn'
Malay (macrolanguage) 'ms' Standard Malay 'zsm'
Swahili (macrolanguage) 'sw' Swahili (individual language) 'swh'
Uzbek 'uz' Northern Uzbek 'uzn'
Figure 8: Macrolanguages closely identified with individual languages
Applications MAY use macrolanguage information to improve matching or
language negotiation. For example, the information that 'sr'
(Serbian) and 'hr' (Croatian) share a macrolanguage expresses a
closer relation between those languages than between, say, 'sr'
(Serbian) and 'ma' (Macedonian). However, this relationship is not
guaranteed nor is it exclusive. For example, Romanian ('ro') and
Moldavian ('mo') do not share a macrolanguage, but are far more
closely related to each other than Cantonese ('yue') and Wu ('wuu') ,
which do share a macrolanguage.
4.2. Meaning of the Language Tag
The meaning of a language tag is related to the meaning of the
subtags that it contains. Each subtag, in turn, implies a certain
range of expectations one might have for related content, although it
is not a guarantee. For example, the use of a script subtag such as
'Arab' (Arabic script) does not mean that the content contains only
Arabic characters. It does mean that the language involved is
predominantly in the Arabic script. Thus a language tag and its
subtags can encompass a very wide range of variation and yet remain
appropriate in each particular instance.
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Validity of a tag is not the only factor determining its usefulness.
While every valid tag has a meaning, it might not represent any real-
world language usage. This is unavoidable in a system in which
subtags can be combined freely. For example, tags such as
"ar-Cyrl-CO" (Arabic, Cyrillic script, as used in Colombia ) or "tlh-
Kore-AQ-fonipa" (Klingon, Korean script, as used in Antarctica, IPA
phonetic transcription) are both valid and unlikely to represent a
useful combination of language attributes.
The meaning of a given tag doesn't depend on the context in which it
appears. The relationship between a tag's meaning and the
information objects to which that tag is applied, however, can vary.
o For a single information object, the associated language tags
might be interpreted as the set of languages that is necessary for
a complete comprehension of the complete object. Example: Plain
text documents.
o For an aggregation of information objects, the associated language
tags could be taken as the set of languages used inside components
of that aggregation. Examples: Document stores and libraries.
o For information objects whose purpose is to provide alternatives,
the associated language tags could be regarded as a hint that the
content is provided in several languages and that one has to
inspect each of the alternatives in order to find its language or
languages. In this case, the presence of multiple tags might not
mean that one needs to be multi-lingual to get complete
understanding of the document. Example: MIME multipart/
alternative.
o In markup languages, such as HTML and XML, language information
can be added to each part of the document identified by the markup
structure (including the whole document itself). For example, one
could write <span lang="fr">C'est la vie.</span> inside a
Norwegian document; the Norwegian-speaking user could then access
a French-Norwegian dictionary to find out what the marked section
meant. If the user were listening to that document through a
speech synthesis interface, this formation could be used to signal
the synthesizer to appropriately apply French text-to-speech
pronunciation rules to that span of text, instead of applying the
inappropriate Norwegian rules.
o Language tags form the basis for most implementations of locale
identifiers. For example, see Unicode's CLDR (Common Locale Data
Repository) project.
Language tags are related when they contain a similar sequence of
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subtags. For example, if a language tag B contains language tag A as
a prefix, then B is typically "narrower" or "more specific" than A.
Thus, "zh-Hant-TW" is more specific than "zh-Hant".
This relationship is not guaranteed in all cases: specifically,
languages that begin with the same sequence of subtags are NOT
guaranteed to be mutually intelligible, although they might be. For
example, the tag "az" shares a prefix with both "az-Latn"
(Azerbaijani written using the Latin script) and "az-Cyrl"
(Azerbaijani written using the Cyrillic script). A person fluent in
one script might not be able to read the other, even though the text
might be identical. Content tagged as "az" most probably is written
in just one script and thus might not be intelligible to a reader
familiar with the other script.
Similarly, not all subtags specify an actual distinction in language.
For example, the tags "en-US" and "en-CA" mean, roughly, English with
features generally thought to be characteristic of the United States
and Canada, respectively. They do not imply that a significant
dialectical boundary exists between any arbitrarily selected point in
the United States and any arbitrarily selected point in Canada.
Neither does a particular region subtag imply that linguistic
distinctions do not exist within that region.
4.3. Lists of Languages
In some applications, a single content item might best be associated
with more than one language tag. Examples of such a usage include:
o A language priority list [RFC4647] describing a user's language
preferences. This is a (possibly weighted) list of potentially-
unrelated varieties, expressing a preference, rather than as a
declaration about actual content.
o Content items that contain multiple, distinct varieties. Often
this is used to indicate an appropriate audience for a given
content item when multiple choices might be appropriate. Examples
of this could include:
* Metadata about the appropriate audience for a movie title. For
example, a DVD might label its individual audio tracks 'de'
(German), 'fr' (French), and 'es' (Spanish), but the overall
title would list "de, fr, es" as its overall audience.
* A French/English, English/French dictionary tagged as both "en"
and "fr" to specify that it applies equally to French and
English
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* A side-by-side or interlinear translation of a document, as is
commonly done with classical works in Latin or Greek
o Content items that contain a single language but which require
multiple levels of specificity. For example, a library might wish
to classify a particular work as both Chinese ('zh') and as Min
Nan ('nan') for audiences capable of appreciating the distinction
or needing to select content more narrowly.
4.4. Length Considerations
There is no defined upper limit on the size of language tags. While
historically most language tags have consisted of language and region
subtags with a combined total length of up to six characters, larger
tags have always been both possible and actually appeared in use.
Neither the language tag syntax nor other requirements in this
document impose a fixed upper limit on the number of subtags in a
language tag (and thus an upper bound on the size of a tag). The
language tag syntax suggests that, depending on the specific
language, more subtags (and thus a longer tag) are sometimes
necessary to completely identify the language for certain
applications; thus, it is possible to envision long or complex subtag
sequences.
4.4.1. Working with Limited Buffer Sizes
Some applications and protocols are forced to allocate fixed buffer
sizes or otherwise limit the length of a language tag. A conformant
implementation or specification MAY refuse to support the storage of
language tags that exceed a specified length. Any such limitation
SHOULD be clearly documented, and such documentation SHOULD include
what happens to longer tags (for example, whether an error value is
generated or the language tag is truncated). A protocol that allows
tags to be truncated at an arbitrary limit, without giving any
indication of what that limit is, has the potential for causing harm
by changing the meaning of tags in substantial ways.
In practice, most language tags do not require more than a few
subtags and will not approach reasonably sized buffer limitations;
see Section 4.1.
Some specifications or protocols have limits on tag length but do not
have a fixed length limitation. For example, [RFC2231] has no
explicit length limitation: the length available for the language tag
is constrained by the length of other header components (such as the
charset's name) coupled with the 76-character limit in [RFC2047].
Thus, the "limit" might be 50 or more characters, but it could
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potentially be quite small.
The considerations for assigning a buffer limit are:
Implementations SHOULD NOT truncate language tags unless the
meaning of the tag is purposefully being changed, or unless the
tag does not fit into a limited buffer size specified by a
protocol for storage or transmission.
Implementations SHOULD warn the user when a tag is truncated since
truncation changes the semantic meaning of the tag.
Implementations of protocols or specifications that are space
constrained but do not have a fixed limit SHOULD use the longest
possible tag in preference to truncation.
Protocols or specifications that specify limited buffer sizes for
language tags MUST allow for language tags of up to 33 characters.
Protocols or specifications that specify limited buffer sizes for
language tags SHOULD allow for language tags of at least 30
characters. Note that RFC 4646 [RFC4646] recommended a field size
of 42 character because it included the permanently reserved (and
unused) 'extlang' production. The current size recommendation
does not include the use of the 'extlang' field. Protocols or
specifications that commonly use extensions or private use subtags
might wish to reserve or recommend a longer "minimum buffer" size.
The following illustration shows how the 30-character recommendation
was derived:
language = 3 (ISO 639-2; ISO 639-1 requires 2)
script = 5 (if not suppressed: see Section 4.1)
region = 4 (UN M.49; ISO 3166-1 requires 3)
variant1 = 9 (needs 'language' as a prefix)
variant2 = 9 (needs 'language-variant1' as a prefix)
total = 30 characters
Figure 9: Derivation of the Limit on Tag Length
4.4.2. Truncation of Language Tags
Truncation of a language tag alters the meaning of the tag, and thus
SHOULD be avoided. However, truncation of language tags is sometimes
necessary due to limited buffer sizes. Such truncation MUST NOT
permit a subtag to be chopped off in the middle or the formation of
invalid tags (for example, one ending with the "-" character).
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This means that applications or protocols that truncate tags MUST do
so by progressively removing subtags along with their preceding "-"
from the right side of the language tag until the tag is short enough
for the given buffer. If the resulting tag ends with a single-
character subtag, that subtag and its preceding "-" MUST also be
removed. For example:
Tag to truncate: zh-Latn-CN-variant1-a-extend1-x-wadegile-private1
1. zh-Latn-CN-variant1-a-extend1-x-wadegile
2. zh-Latn-CN-variant1-a-extend1
3. zh-Latn-CN-variant1
4. zh-Latn-CN
5. zh-Latn
6. zh
Figure 10: Example of Tag Truncation
4.5. Canonicalization of Language Tags
Since a particular language tag is sometimes used by many processes,
language tags SHOULD always be created or generated in a canonical
form.
A language tag is in canonical form when:
1. The tag is well-formed according the rules in Section 2.1 and
Section 2.2.
2. Subtags of type 'Region' that have a Preferred-Value mapping in
the IANA registry (see Section 3.1) MUST be replaced with their
mapped value.
3. Redundant or grandfathered tags that have a Preferred-Value
mapping in the IANA registry (see Section 3.1) MUST be replaced
with their mapped value. These items either are deprecated
mappings created before the adoption of this document (such as
the mapping of "no-nyn" to "nn" or "i-klingon" to "tlh") or are
the result of later registrations or additions to this document
(for example, "zh-hakka" was deprecated in favor of the ISO 639-3
code 'hak' when this document was adopted).
4. Other subtags that have a Preferred-Value mapping in the IANA
registry (see Section 3.1) MUST be replaced with their mapped
value. These items consist entirely of clerical corrections to
ISO 639-1 in which the deprecated subtags have been maintained
for compatibility purposes.
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5. If more than one extension subtag sequence exists, the extension
sequences are ordered into case-insensitive ASCII order by
singleton subtag.
Example: The language tag "en-a-aaa-b-ccc-bbb-x-xyz" is in canonical
form, while "en-b-ccc-bbb-a-aaa-X-xyz" is well-formed and potentially
valid (extensions 'a' and 'b' are not defined as of the publication
of this document) but not in canonical form (the extensions are not
in alphabetical order).
Example: The language tag "en-BU" (English as used in Burma) is not
canonical because the 'BU' subtag has a canonical mapping to 'MM'
(Myanmar), although the tag "en-BU" maintains its validity.
Canonicalization of language tags does not imply anything about the
use of upper or lowercase letters when processing or comparing
subtags (and as described in Section 2.1). All comparisons MUST be
performed in a case-insensitive manner.
When performing canonicalization of language tags, processors MAY
regularize the case of the subtags (that is, this process is
OPTIONAL), following the case used in the registry. Note that this
corresponds to the following casing rules: uppercase all non-initial
two-letter subtags; titlecase all non-initial four-letter subtags;
lowercase everything else.
Note: Case folding of ASCII letters in certain locales, unless
carefully handled, sometimes produces non-ASCII character values.
The Unicode Character Database file "SpecialCasing.txt" defines the
specific cases that are known to cause problems with this. In
particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is
uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE).
Implementers SHOULD specify a locale-neutral casing operation to
ensure that case folding of subtags does not produce this value,
which is illegal in language tags. For example, if one were to
uppercase the region subtag 'in' using Turkish locale rules, the
sequence U+0130 U+004E would result instead of the expected 'IN'.
Note: if the field 'Deprecated' appears in a registry record without
an accompanying 'Preferred-Value' field, then that tag or subtag is
deprecated without a replacement. Validating processors SHOULD NOT
generate tags that include these values, although the values are
canonical when they appear in a language tag.
An extension MUST define any relationships that exist between the
various subtags in the extension and thus MAY define an alternate
canonicalization scheme for the extension's subtags. Extensions MAY
define how the order of the extension's subtags are interpreted. For
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example, an extension could define that its subtags are in canonical
order when the subtags are placed into ASCII order: that is, "en-a-
aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension might
define that the order of the subtags influences their semantic
meaning (so that "en-b-ccc-bbb-aaa" has a different value from "en-b-
aaa-bbb-ccc"). However, extension specifications SHOULD be designed
so that they are tolerant of the typical processes described in
Section 3.7.
4.6. Considerations for Private Use Subtags
Private use subtags, like all other subtags, MUST conform to the
format and content constraints in the ABNF. Private use subtags have
no meaning outside the private agreement between the parties that
intend to use or exchange language tags that employ them. The same
subtags MAY be used with a different meaning under a separate private
agreement. They SHOULD NOT be used where alternatives exist and
SHOULD NOT be used in content or protocols intended for general use.
Private use subtags are simply useless for information exchange
without prior arrangement. The value and semantic meaning of private
use tags and of the subtags used within such a language tag are not
defined by this document.
Subtags defined in the IANA registry as having a specific private use
meaning convey more information that a purely private use tag
prefixed by the singleton subtag 'x'. For applications, this
additional information MAY be useful.
For example, the region subtags 'AA', 'ZZ', and in the ranges
'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166-1 private use codes)
MAY be used to form a language tag. A tag such as "zh-Hans-XQ"
conveys a great deal of public, interchangeable information about the
language material (that it is Chinese in the simplified Chinese
script and is suitable for some geographic region 'XQ'). While the
precise geographic region is not known outside of private agreement,
the tag conveys far more information than an opaque tag such as
"x-someLang", which contains no information about the language subtag
or script subtag outside of the private agreement.
However, in some cases content tagged with private use subtags MAY
interact with other systems in a different and possibly unsuitable
manner compared to tags that use opaque, privately defined subtags,
so the choice of the best approach sometimes depends on the
particular domain in question.
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5. IANA Considerations
This section deals with the processes and requirements necessary for
IANA to undertake to maintain the subtag and extension registries as
defined by this document and in accordance with the requirements of
[RFC2434].
The impact on the IANA maintainers of the two registries defined by
this document will be a small increase in the frequency of new
entries or updates. IANA also is required to create a new mailing
list (described below in Section 5.1) to announce registry changes
and updates.
5.1. Language Subtag Registry
Upon adoption of this document, IANA will update the registry using
instructions and content provided in a companion document:
[registry-update]. The criteria and process for selecting the
updated set of records are described in that document. The updated
set of records represents no impact on IANA, since the work to create
it will be performed externally.
Future work on the Language Subtag Registry includes the following
activities:
o Inserting or replacing whole records. These records are
preformatted for IANA by the Language Subtag Reviewer, as
described in Section 3.3.
o Archiving and making publicly available the registration forms.
o Announcing each updated version of the registry on the
"ietf-languages-announcements@iana.org" mailing list.
Each registration form sent to IANA contains a single record for
incorporation into the registry. The form will be sent to
"iana@iana.org" by the Language Subtag Reviewer. It will have a
subject line indicating whether the enclosed form represents an
insertion of a new record (indicated by the word "INSERT" in the
subject line) or a replacement of an existing record (indicated by
the word "MODIFY" in the subject line). At no time can a record be
deleted from the registry.
IANA will extract the record from the form and place the inserted or
modified record into the appropriate section of the language subtag
registry, grouping the records by their 'Type' field. Inserted
records can be placed anywhere in the appropriate section; there is
no guarantee of the order of the records beyond grouping them
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together by 'Type'. Modified records overwrite the record they
replace.
Whenever an entry is created or modified in the registry, the 'File-
Date' record at the start of the registry is updated to reflect the
most recent modification date in the [RFC3339] "full-date" format:
included in any request to insert or modify records will be a new
File-Date record indicating the acceptance date of the record. This
record is to be placed first in the registry, replacing the existing
File-Date record. In the event that the File-Date record present in
the registry has a later date than the record being inserted or
modified, then the latest (most recent) record will be preserved.
IANA should attempt to process multiple registration requests in
order according to the File-Date in the form, since one registration
could otherwise cause a more recent change to be overwritten.
The updated registry file MUST use the UTF-8 character encoding and
IANA MUST check the registry file for proper encoding. Non-ASCII
characters can be sent to IANA by attaching the registration form to
the email message or by using various encodings in the mail message
body (UTF-8 is recommended). IANA will verify any unclear or
corrupted characters with the Language Subtag Reviewer prior to
posting the updated registry.
IANA will also archive and make publicly available from
"http://www.iana.org/assignments/lang-subtags-templates/" each
registration form. Note that multiple registrations can pertain to
the same record in the registry.
Developers who are dependent upon the language subtag registry
sometimes would like to be informed of changes in the registry so
that they can update their implementations. When any change is made
to the language subtag registry, IANA will send an announcement
message to "ietf-languages-announcements@iana.org" (a self-
subscribing list that only IANA can post to).
5.2. Extensions Registry
The Language Tag Extensions Registry can contain at most 35 records
and thus changes to this registry are expected to be very infrequent.
Future work by IANA on the Language Tag Extensions Registry is
limited to two cases. First, the IESG MAY request that new records
be inserted into this registry from time to time. These requests
MUST include the record to insert in the exact format described in
Section 3.7. In addition, there MAY be occasional requests from the
maintaining authority for a specific extension to update the contact
information or URLs in the record. These requests MUST include the
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complete, updated record. IANA is not responsible for validating the
information provided, only that it is properly formatted. It should
reasonably be seen to come from the maintaining authority named in
the record present in the registry.
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6. Security Considerations
Language tags used in content negotiation, like any other information
exchanged on the Internet, might be a source of concern because they
might be used to infer the nationality of the sender, and thus
identify potential targets for surveillance.
This is a special case of the general problem that anything sent is
visible to the receiving party and possibly to third parties as well.
It is useful to be aware that such concerns can exist in some cases.
The evaluation of the exact magnitude of the threat, and any possible
countermeasures, is left to each application protocol (see BCP 72
[RFC3552] for best current practice guidance on security threats and
defenses).
The language tag associated with a particular information item is of
no consequence whatsoever in determining whether that content might
contain possible homographs. The fact that a text is tagged as being
in one language or using a particular script subtag provides no
assurance whatsoever that it does not contain characters from scripts
other than the one(s) associated with or specified by that language
tag.
Since there is no limit to the number of variant, private use, and
extension subtags, and consequently no limit on the possible length
of a tag, implementations need to guard against buffer overflow
attacks. See Section 4.4 for details on language tag truncation,
which can occur as a consequence of defenses against buffer overflow.
Although the specification of valid subtags for an extension (see
Section 3.7) MUST be available over the Internet, implementations
SHOULD NOT mechanically depend on it being always accessible, to
prevent denial-of-service attacks.
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7. Character Set Considerations
The syntax in this document requires that language tags use only the
characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most
character sets, so the composition of language tags should not have
any character set issues.
Rendering of characters based on the content of a language tag is not
addressed in this memo. Historically, some languages have relied on
the use of specific character sets or other information in order to
infer how a specific character should be rendered (notably this
applies to language- and culture-specific variations of Han
ideographs as used in Japanese, Chinese, and Korean). When language
tags are applied to spans of text, rendering engines sometimes use
that information in deciding which font to use in the absence of
other information, particularly where languages with distinct writing
traditions use the same characters.
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8. Changes from RFC 4646
The main goal for this revision of this document was to incorporate
ISO 639-3 and its attendant set of language codes into the IANA
Language Subtag Registry, permitting the identification of many more
languages and dialects than previously supported.
The specific changes in this document to meet these goals are:
o Defines the incorporation of ISO 639-3 codes as language. It also
permanently reserves and disallows the use of extlang subtags.
The changes necessary to achieve this were:
* Modified the ABNF comments.
* Updated various registration and stability requirements
sections to reference ISO 639-3 in addition to ISO 639-1 and
ISO 639-2.
* Edited the text to eliminate references to extended language
subtags where they are no longer used.
* Explained the change in the section on extended language
subtags.
o Changed the ABNF related to grandfathered tags. The irregular
tags are now listed. Well-formed grandfathered tags are now
described by the 'langtag' production and the 'grandfathered'
production was removed as a result. Also: added description of
both types of grandfathered tags to Section 2.2.8.
o Added the paragraph on "collections" to Section 4.1.
o Changed the capitalization rules for 'Tag' fields in Section 3.1.
o Split section 3.1 up into subsections.
o Modified section 3.5 to allow Suppress-Script fields to be added,
modified, or removed via the registration process. This was an
erratum from RFC 4646.
o Modified examples that used region code 'CS' (formerly Serbia and
Montenegro) to use 'RS' (Serbia) instead.
o Modified the rules for creating and maintaining record
'Description' fields to prevent duplicates, including inverted
duplicates.
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o Removed the lengthy description of why RFC 4646 was created from
this section, which also caused the removal of the reference to
XML Schema.
o Modified the text in section 2.1 to place more emphasis on the
fact that language tags are not case sensitive.
o Replaced the example "fr-Latn-CA" in Section 2.1 with "sr-Latn-RS"
and "az-Arab-IR" because "fr-Latn-CA" doesn't respect the
Suppress-Script on 'Latn' with 'fr'.
o Changed the requirements for well-formedness to make singleton
repetition checking optional (it is required for validity
checking) in Section 2.2.9.
o Changed the text in Section 2.2.9 referring to grandfathered
checking to note that the list is now included in the ABNF.
o Modified and added text to Section 3.2. The job description was
placed first. A note was added making clear that the Language
Subtag Reviewer may delegate various non-critical duties,
including list moderation. Finally, additional text was added to
make the appointment process clear and to clarify that decisions
and performance of the reviewer are appealable.
o Added text to Section 3.5 clarifying that the ietf-languages list
is operated by whomever the IESG appoints.
o Added text to Section 3.1.4 clarifying that the first Description
in a 'language' record matches the corresponding Reference Name
for the language in ISO 639-3.
o Modified Section 2.2.9 to define classes of conformance related to
specific tags (formerly 'well-formed' and 'valid' referred to
implementations). Notes were added about the removal of 'extlang'
from the ABNF provided in RFC 4646, allowing for well-formedness
using this older definition. Reference to RFC 3066 well-
formedness was also added.
o Added text to the end of Section 3.1.2 noting that future versions
of this document might add new field types to the Registry format
and recommending that implementations ignore any unrecognized
fields.
o Added text about what the lack of a Suppress-Script field means in
a record to Section 3.1.8.
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o Added text allowing the correction of misspellings and typographic
errors to Section 3.1.4.
o Added text to Section 3.1.7 disallowing Prefix field conflicts
(such as circular prefix references).
o Modified text in Section 3.5 to require the subtag reviewer to
announce his/her decision (or extension) following the two-week
period. Also clarified that any decision or failure to decide can
be appealed.
o Modified text in Section 4.1 to include the (heretofore anecdotal)
guiding principle of tag choice, and clarifying the non-use of
script subtags in non-written applications. Also updated examples
in this section to use Chamic languages as an example of language
collections.
o Prohibited multiple use of the same variant in a tag (i.e. "de-
1901-1901"). Previously this was only a recommendation
("SHOULD").
o Removed inappropriate [RFC2119] language from the illustration in
Section 4.4.1.
o Replaced the example of deprecating "zh-gouyu" with "zh-
hakka"->"hak" in Section 4.5, noting that it was this document
that caused the change.
o Replaced the section in Section 4.1 dealing with "mul"/"und" to
include the subtags 'zxx' and 'mis', as well as the tag
"i-default". A normative reference to RFC 2277 was added, along
with an informative reference to MARC21.
o Added text to Section 3.5 clarifying that any modifications of a
registration request must be sent to the ietf-languages list
before submission to IANA.
o Changed the ABNF for the record-jar format from using the LWSP
production to use a folding whitespace production similar to obs-
FWS in [RFC5234]. This effectively prevents unintentional blank
lines inside a field.
o Clarified and revised text in Section 3.3, Section 3.5, and
Section 5.1 to clarify that the Language Subtag Reviewer sends the
complete registration forms to IANA, that IANA extracts the record
from the form, and that the forms must also be archived separately
from the registry.
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o Added text to Section 5 requiring IANA to send an announcement to
an ietf-languages-announce list whenever the registry is updated.
o Modification of the registry to use UTF-8 as its character
encoding. This also entails additional instructions to IANA and
the Language Subtag Reviewer in the registration process.
o Modified the rules in Section 2.2.4 so that "exceptionally
reserved" ISO 3166-1 codes other than 'UK' were included into the
registry. In particular, this allows the code 'EU' (European
Union) to be used to form language tags or (more commonly) for
applications that use the registry for region codes to reference
this subtag.
o Modified the IANA considerations section (Section 5) to remove
unnecessary normative [RFC2119] language.
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9. References
9.1. Normative References
[ISO15924]
International Organization for Standardization, "ISO
15924:2004. Information and documentation -- Codes for the
representation of names of scripts", January 2004.
[ISO3166-1]
International Organization for Standardization, "ISO 3166-
1:2006. Codes for the representation of names of countries
and their subdivisions -- Part 1: Country codes",
November 2006.
[ISO639-1]
International Organization for Standardization, "ISO 639-
1:2002. Codes for the representation of names of languages
-- Part 1: Alpha-2 code", 2002.
[ISO639-2]
International Organization for Standardization, "ISO 639-
2:1998. Codes for the representation of names of languages
-- Part 2: Alpha-3 code, first edition", 1998.
[ISO639-3]
International Organization for Standardization, "ISO 639-
3:2007. Codes for the representation of names of languages
-- Part 3: Alpha-3 code for comprehensive coverage of
languages", 2007.
[ISO646] International Organization for Standardization, "ISO/IEC
646:1991, Information technology -- ISO 7-bit coded
character set for information interchange.", 1991.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in
the IETF Standards Process", BCP 11, RFC 2028,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
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[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
Understanding Concerning the Technical Work of the
Internet Assigned Numbers Authority", RFC 2860, June 2000.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC4645] Ewell, D., "Initial Language Subtag Registry", RFC 4645,
September 2006.
[RFC4647] Phillips, A. and M. Davis, "Matching of Language Tags",
BCP 47, RFC 4647, September 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[UAX14] Freitag, A., "Unicode Standard Annex #14: Line Breaking
Properties", August 2006,
<http://www.unicode.org/reports/tr14/>.
[UN_M.49] Statistics Division, United Nations, "Standard Country or
Area Codes for Statistical Use", UN Standard Country or
Area Codes for Statistical Use, Revision 4 (United Nations
publication, Sales No. 98.XVII.9, June 1999.
9.2. Informative References
[RFC1766] Alvestrand, H., "Tags for the Identification of
Languages", RFC 1766, March 1995.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions:
Character Sets, Languages, and Continuations", RFC 2231,
November 1997.
[RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO
10646", RFC 2781, February 2000.
[RFC3066] Alvestrand, H., "Tags for the Identification of
Languages", RFC 3066, January 2001.
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[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4646] Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 4646, September 2006.
[UTS35] Davis, M., "Unicode Technical Standard #35: Locale Data
Markup Language (LDML)", December 2007,
<http://www.unicode.org/reports/tr35/>.
[Unicode] Unicode Consortium, "The Unicode Consortium. The Unicode
Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003.
ISBN 0-321-49081-0)", January 2007.
[iso639.prin]
ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory
Committee: Working principles for ISO 639 maintenance",
March 2000,
<http://www.loc.gov/standards/iso639-2/
iso639jac_n3r.html>.
[record-jar]
Raymond, E., "The Art of Unix Programming", 2003,
<urn:isbn:0-13-142901-9>.
[registry-update]
Ewell, D., Ed., "Update to the Language Subtag Registry",
September 2006, <http://www.ietf.org/internet-drafts/
draft-ietf-ltru-initial-registry-00.txt>.
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Appendix A. Acknowledgements
Any list of contributors is bound to be incomplete; please regard the
following as only a selection from the group of people who have
contributed to make this document what it is today.
The contributors to RFC 4646, RFC 4647, RFC 3066, and RFC 1766, the
precursors of this document, made enormous contributions directly or
indirectly to this document and are generally responsible for the
success of language tags.
The following people contributed to this document:
Stephane Bortzmeyer, Karen Broome, Peter Constable, John Cowan,
Martin Duerst, Frank Ellerman, Doug Ewell, Deborah Garside, Marion
Gunn, Kent Karlsson, Chris Newman, Randy Presuhn, Stephen Silver, and
many, many others.
Very special thanks must go to Harald Tveit Alvestrand, who
originated RFCs 1766 and 3066, and without whom this document would
not have been possible.
Special thanks go to Michael Everson, who served as the Language Tag
Reviewer for almost the entire RFC 1766/RFC 3066 period, as well as
the Language Subtag Reviewer since the adoption of RFC 4646.
Special thanks also to Doug Ewell, for his production of the first
complete subtag registry, his work to support and maintain new
registrations, and his careful editorship of both RFC 4645 and
[registry-update].
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Appendix B. Examples of Language Tags (Informative)
Simple language subtag:
de (German)
fr (French)
ja (Japanese)
i-enochian (example of a grandfathered tag)
Language subtag plus Script subtag:
zh-Hant (Chinese written using the Traditional Chinese script)
zh-Hans (Chinese written using the Simplified Chinese script)
sr-Cyrl (Serbian written using the Cyrillic script)
sr-Latn (Serbian written using the Latin script)
Language-Script-Region:
zh-Hans-CN (Chinese written using the Simplified script as used in
mainland China)
sr-Latn-RS (Serbian written using the Latin script as used in
Serbia)
Language-Variant:
sl-rozaj (Resian dialect of Slovenian)
sl-nedis (Nadiza dialect of Slovenian)
Language-Region-Variant:
de-CH-1901 (German as used in Switzerland using the 1901 variant
[orthography])
sl-IT-nedis (Slovenian as used in Italy, Nadiza dialect)
Language-Script-Region-Variant:
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hy-Latn-IT-arevela (Eastern Armenian written in Latin script, as
used in Italy)
Language-Region:
de-DE (German for Germany)
en-US (English as used in the United States)
es-419 (Spanish appropriate for the Latin America and Caribbean
region using the UN region code)
Private use subtags:
de-CH-x-phonebk
az-Arab-x-AZE-derbend
Private use registry values:
x-whatever (private use using the singleton 'x')
qaa-Qaaa-QM-x-southern (all private tags)
de-Qaaa (German, with a private script)
sr-Latn-QM (Serbian, Latin-script, private region)
sr-Qaaa-RS (Serbian, private script, for Serbia)
Tags that use extensions (examples ONLY: extensions MUST be defined
by revision or update to this document or by RFC):
en-US-u-islamCal
zh-CN-a-myExt-x-private
en-a-myExt-b-another
Some Invalid Tags:
de-419-DE (two region tags)
a-DE (use of a single-character subtag in primary position; note
that there are a few grandfathered tags that start with "i-" that
are valid)
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ar-a-aaa-b-bbb-a-ccc (two extensions with same single-letter
prefix)
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Appendix C. Examples of Registration Forms
LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester: Han Steenwijk
2. E-mail address of requester: han.steenwijk @ unipd.it
3. Record Requested:
Type: variant
Subtag: biske
Description: The San Giorgio dialect of Resian
Description: The Bila dialect of Resian
Prefix: sl-rozaj
Comments: The dialect of San Giorgio/Bila is one of the
four major local dialects of Resian
4. Intended meaning of the subtag: The local variety of Resian as
spoken in San Giorgio/Bila
5. Reference to published description of the language (book or
article):
-- Jan I.N. Baudouin de Courtenay - Opyt fonetiki rez'janskich
govorov, Varsava - Peterburg: Vende - Kozancikov, 1875.
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LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester: Jaska Zedlik
2. E-mail address of requester: jz53 @ zedlik.com
3. Record Requested:
Type: variant
Subtag: tarask
Description: Belarusian in Taraskievica orthography
Prefix: be
Comments: The subtag represents Branislau Taraskievic's Belarusian
orthography as published in "Bielaruski klasycny pravapis" by Juras
Buslakou, Vincuk Viacorka, Zmicier Sanko, and Zmicier Sauka
(Vilnia-Miensk 2005).
4. Intended meaning of the subtag:
The subtag is intended to represent the Belarusian orthography as
published in "Bielaruski klasycny pravapis" by Juras Buslakou, Vincuk
Viacorka, Zmicier Sanko, and Zmicier Sauka (Vilnia-Miensk 2005).
5. Reference to published description of the language (book or article):
Taraskievic, Branislau. Bielaruskaja gramatyka dla skol. Vilnia: Vyd.
"Bielaruskaha kamitetu", 1929, 5th edition.
Buslakou, Juras; Viacorka, Vincuk; Sanko, Zmicier; Sauka, Zmicier.
Bielaruski klasycny pravapis. Vilnia-Miensk, 2005.
6. Any other relevant information:
Belarusian in Taraskievica orthography became widely used, especially in
Belarusian-speaking Internet segment, but besides this some books and
newspapers are also printed using this orthography of Belarusian.
Phillips & Davis Expires November 17, 2008 [Page 75]
Internet-Draft language-tags May 2008
Authors' Addresses
Addison Phillips (editor)
Lab126
Email: addison@inter-locale.com
URI: http://www.inter-locale.com
Mark Davis (editor)
Google
Email: mark.davis@google.com
Phillips & Davis Expires November 17, 2008 [Page 76]
Internet-Draft language-tags May 2008
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