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W3C

Language Tags and Locale Identifiers for the World Wide Web

W3C Working Draft 12 June 2006

This version:
http://www.w3.org/TR/2006/WD-ltli-20060612/
Latest version:
http://www.w3.org/TR/ltli/
Previous version:
http://www.w3.org/TR/2006/WD-ltli-20060419/
Editor:
Felix Sasaki, W3C

This document is also available in these non-normative formats: XML.


Abstract

Based on [RFC 3066bis] and [RFC 3066bis Matching], this document describes mechanisms for identifying or selecting the language of content or locale preferences used to process information using Web technologies. It describes how document formats, specifications, and implementations should handle language tags, as well as data structures that extend these tags to describe international preferences.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This is an updated Public Working Draft of "Language and Locale Identifiers for the World Wide Web (LTLI)".

This document describes mechanisms for identifying or selecting the language of content or locale preferences used to process information using Web technologies. It describes how document formats, specifications, and implementations should handle language tags, as well as data structures that extend these tags to describe international preferences.

This document was developed by the Internationalization Core Working Group, part of the W3C Internationalization Activity. The Working Group expects to advance this Working Draft to Recommendation Status. A complete list of changes to this document is available.

Send your comments to www-i18n-comments@w3.org. Use "[Comments on ltli WD]" in the subject line of your email, followed by a brief subject. The archives for this list are publicly available.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

Appendices

A Normative References
B References (Non-Normative)
C Revision Log (Non-Normative)

Go to the table of contents.1 Introduction

This section is informative.

Go to the table of contents.1.1 Scope of this Specification

This document describes mechanisms for identifying or selecting the language of content or locale preferences used to process information using Web technologies. It describes how document formats, specifications, and implementations should handle the language tags described by [BCP 47], as well as data structures that extend these tags to describe international preferences (see sec. 3.1 in [WS-I18N Scenarios]).

Identification of language and locale has a broad range of applications within the World Wide Web. Existing standards which make use of language identification includes the xml:lang attribute in [XML 1.0], the lang and hreflang atttributes in [HTML 4.01], or the language property in [XSL 1.0]. Locale identification is used for example within the CLDR project, cf. [LDML].

The current best practice when developing specifications for language identification is to refer to [RFC 3066], using a formulation like "RFC 3066 or its successor". Recently a successor for [RFC 3066] has been developed, called [RFC 3066bis]. This specification takes [RFC 3066bis] as the basis for language identification, and [RFC 3066bis Matching] as the basis for matching of language identifiers ("tags").

The current practice in many standards is to identify language in terms of [RFC 3066], using formulations like "RFC 3066 or its successor". Recently a successor for [RFC 3066] has been developed, called [RFC 3066bis]. This specification takes [RFC 3066bis] as the basis for language identification, and [RFC 3066bis Matching] as the basis for matching of language tags.

[RFC 3066bis] refers to language identification only. Locales can be identified in several ways. One method is by inference from language tags. For example, an implementation could map a language tag from an existing protocol, such as HTTP's Accept-Language header, to its locale model. Locales may also be identified directly by using the language tag syntax in data items (elements, attributes, headers, etc.) that explicitly serve the purpose of locale identification.

Currently, this specification refers to [RFC 3066bis] and [RFC 3066bis Matching] directly. Since [RFC 3066bis] and [RFC 3066bis Matching] are expected to become the new BCP 47 before this working draft becomes a recommendation, a later draft of this specification will refer to BCP 47 directly.

Go to the table of contents.1.2 Out of Scope

This specification will not deal with formats for locale data or actual locale data. One possible source of locale data and data formats is [LDML].

Go to the table of contents.1.3 Application Scenario: Web Services Internationalization

In order to enable multi-locale operation of Web services and to create the ability for locale negotiation, this specification describes a standardized method for identifying locales and locale and/or language tags on the Web, including non-normative guidelines for implementation. This is called out in Requirement R005 of [WS-I18N Req]. The mechanism for language and locale identification which is defined in this specification will be used in a future version of the description of Web services Internationalization in [WS-I18N].

Further application scenarios of this specification encompass for example the standards mentioned in Section 1.1: Scope of this Specification. The scenarios can be divided in four areas:

  • Definition of values for language tags

  • Definition of values for locale identifiers

  • Definition of matching schemes for language tags

  • Definition of matching schemes for locale identifiers

As for matching of language tags, many specifications already define operations using matching. An example is the language pseudo-class :lang defined in sec. 5.11.4 of [CSS 2.1]. It matches elements based on their language. This specification formulates requirements on such operations, based on [RFC 3066bis Matching].

Go to the table of contents.1.4 Locale versus Natural Language

This document defines locale identifiers for use in Web technologies. Historically, natural language identifiers [RFC 3066bis] have been used as locale identifiers by some programming languages or operating environments, which is natural since locale identifiers usually share certain core features related to natural language and country/region. This specification defines locale identifiers that specific locale implementations can map to their proprietary features in order to create functional, interoperable applications.

The minimal requirement is the ability to specify the natural language; thus there is industry convergence on the use of [RFC 3066bis] as the core of a locale identifier. For example, [CLDR] uses [RFC 3066bis] as the core of a locale identifier, and provides syntax for extensions for non-linguistic information, such as preferred currency or timezone.

A major difference between language tags and locale identifiers is the meaning of the region code. In both language tags and locales, the region code indicates variation in language (as with regional dialects) or presentation and format (such as number or date formats). In a locale, the region code is also sometimes used to indicate the physical location, market, legal, or other governing policies for the user.

The language tag may be available in several places. In HTTP, there is an Accept-Language header field which can be used. MIME has a Content-Language header which contains a language tag. In XML, there is an attribute which can be defined for elements called xml:lang. xml:lang marks all the contents and attribute values of the corresponding element as belonging to the language identified. What that means for processing those contents varies from application to application.

For more detailed information on the behavior of xml:lang, see [XML 1.0].

Go to the table of contents.2 Notation and Terminology

This section is normative.

Go to the table of contents.2.1 Language Tags and Matching of Language Tags

This document uses the terms language tag and subtag which are defined in [RFC 3066bis].

In addition, this document uses the following terms, which are defined in [RFC 3066bis Matching]:

Example 1: Basic versus extended language range and language priority list

de-de is a basic language range. It matches e.g. the language tag de-DE-1996, but not the language tag de-Deva.

de-*-DE is an extended language range. It matches all of the following tags:

  • de-DE

  • de-DE-x-goethe

  • de-Latn-DE-1996

"en; fr; zh-Hant" is a language priority list. It would be read as "English before French before Chinese as written in the Traditional script". Note that the syntax shown is only an example, since it depends on the protocol, application, or implementation that uses the list.

Go to the table of contents.3 Conformance

This section is normative

This section explains the conditions that specifications have to fulfill to be able to claim conformance to this specification.

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119].

Go to the table of contents.4 Language Tags and Locale Values

This section is normative

The following requirements are formulated for specifications who deal with language tags and locale values or matching schemes.

  1. Specifications that make use of language tags or locale values MUST meet the conformance criteria defined for "well-formed" processors, as defined in sec. 2.2.9 of [RFC 3066bis].

  2. Specifications that make use of language tags or locale values MAY validate these values. If they do so, they MUST meet the conformance criteria defined for "validating" processors, as defined in sec. 2.2.9 of [RFC 3066bis].

  3. Specifications that define operations on language tags or locale values using matching Must use either a basic language range or an extended language range.

  4. Specifications that define operations on language tags or locale values using matching MUST specify whether the resulting language priority list contains a single result (lookup as defined in [RFC 3066bis Matching]), or a possible empty set of results (filtering as defined in [RFC 3066bis Matching]).

Note: Many specifications which have been created before [RFC 3066bis] and [RFC 3066bis Matching] are conformant to these criteria. The purpose of the criteria is to provide a stable source for requirements for language and locale identification.

Go to the table of contents.5 Guidelines for the Interoperable Implementation of this Specification

This section is informative.

[Ed. note: This section will be written in a subsequent working draft.]

Go to the table of contents.A Normative References

BCP 47
Tags for the Identification of Languages. IETF Best Common Practice. BCP 47 is currently represented by [RFC 3066].
RFC 2119
S. Bradner. Key Words for use in RFCs to Indicate Requirement Levels. IETF March 1997. Available at http://www.ietf.org/rfc/rfc2119.txt.
RFC 3066bis
Addison Phillips, Mark Davis. Tags for the Identification of Languages. IETF Internet-Draft, 14 October 2005. See http://www.ietf.org/internet-drafts/draft-ietf-ltru-registry-14.txt.
RFC 3066bis Matching
Addison Phillips, Mark Davis Matching of Language Tags. IETF Internet-Draft, June 2006. See http://www.ietf.org/internet-drafts/draft-ietf-ltru-matching-14.txt.
RFC 3987
Martin Dürst, Michael Suignard. Internationalized Resource Identifiers (IRIs). IETF January 2005. Available at http://www.ietf.org/rfc/rfc3987.txt.

Go to the table of contents.B References (Non-Normative)

CLDR
Common Locale Data Registry (CLDR). Available at http://unicode.org/cldr/.
CSS 2.1
Bert Bos, Tantek Çelik, Ian Hickson, Håkon Wium Lie. Cascading Style Sheets, level 2 revision 1. W3C Working Draft 13 June 2005. Available at http://www.w3.org/TR/2005/WD-CSS21-20050613/. The latest version of CSS 2.1 is available at http://www.w3.org/TR/CSS21/.
HTML 4.01
Dave Ragget, Arnaud Le Hors, Ian Jacobs, eds. HTML 4.01 Specification. W3C Recommendation 24 December 1999. Available at http://www.w3.org/TR/1999/REC-html401-19991224/. The latest version of HTML 4.01 is available at http://www.w3.org/TR/html401/.
LDML
Mark Davis. Locale Data Markup Language (LDML), Unicode Technical Standard #35. Available at http://unicode.org/reports/tr35/tr35-5.html. The latest version of LDML is available at http://unicode.org/reports/tr35/.
RFC 3066
H. Alvestrand, editor. Tags for the Identification of Languages, IETF January 2001. Available at http://www.ietf.org/rfc/rfc3066.txt.
WS-I18N
Addison Phillips, Mary Trumble. Web Services Internationalization (WS-I18N). W3C Working Draft 14 September 2005. Available at http://www.w3.org/TR/2005/WD-ws-i18n-20050914/. The latest version of WS i18n is available at http://www.w3.org/TR/ws-i18n/.
WS-I18N Req
Addison Phillips. Requirements for the Internationalization of Web Services. W3C Working Group Note 16 November 2004. Available at http://www.w3.org/TR/2004/NOTE-ws-i18n-req-20041116/. The latest version of Ws i18n Req is available at http://www.w3.org/TR/ws-i18n-req/.
WS-I18N Scenarios
Debasish Banerjee, Martin Dürst, Mike McKenna, Addison Phillips, Takao Suzuki, Tex Texin, Mary Trumble, Andrea Vine, Kentaro Noji. Web Services Internationalization Usage Scenarios. W3C Working Group Note 30 July 2004. Available at http://www.w3.org/TR/2004/NOTE-ws-i18n-scenarios-20040730/. The latest version of WS i18n Scenarios is available at http://www.w3.org/TR/ws-i18n-scenarios/.
XML 1.0
Tim Bray, Jean Paoli, C.M. Sperberg-McQueen, et al., eds. Extensible Markup Language (XML) 1.0 (Third Edition), W3C Recommendation 04 February 2004. Available at http://www.w3.org/TR/2004/REC-xml-20040204/. The latest version of XML 1.0 is available at http://www.w3.org/TR/REC-xml/.
XSL 1.0
Sharon Adler et al., eds. Extensible Stylesheet Language (XSL) Version 1.0. W3C Recommendation 15 October 2001. Available at http://www.w3.org/TR/2001/REC-xsl-20011015/. The latest version of XSL 1.0 is available at http://www.w3.org/TR/xsl/.

Go to the table of contents.C Revision Log (Non-Normative)

The following log records changes that have been made to this document since the publication in April 2006.