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An IETF language tag is an abbreviated language code (for example, ''en'' for English, ''pt-BR'' for Brazilian Portuguese, or ''nan-Hant-TW'' for Min Nan Chinese as spoken in Taiwan using traditional Han characters) defined by the Internet Engineering Task Force (IETF) in the ''BCP 47'' document series, which is currently composed of normative RFC 5646 (referencing the related RFC 5645) and RFC 4647, along with the normative content of the ''IANA Language Subtag Registry''.〔http://www.iana.org/assignments/language-subtag-registry〕〔(【引用サイトリンク】title=Language subtag lookup app: )〕〔http://www.iana.org/assignments/language-tag-extensions-registry〕〔(【引用サイトリンク】title=IANA — Protocol Registries )〕 Components of language tags are drawn from ISO 639, ISO 15924, ISO 3166-1, and UN M.49. These language tags are used in a number of modern computing standards, including those from the IETF related to the Internet protocols such as HTTP,〔(【引用サイトリンク】title=RFC 7231 - Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content )〕 those from the World Wide Web Consortium such as HTML,〔(【引用サイトリンク】title=Language information and text direction )〕 XML〔(【引用サイトリンク】title=Extensible Markup Language (XML) 1.0 (Fifth Edition) )〕 and PNG,〔(【引用サイトリンク】title=Portable Network Graphics (PNG) Specification (Second Edition) )〕 and those from other private standardization bodies such as SGML or Unicode (in some of its standard annexes), or from national or regional standard bodies like ANSI or ECMA (for example in some of their standards related to computing languages, or to bibliographic references and documents classification used in institutional libraries). == History == IETF language tags were first defined in RFC 1766, published in March 1995. The tags used ISO 639 two-letter language codes and ISO 3166 two-letter country codes, and allowed registration of whole tags that included variant or script subtags of three to eight letters. In January 2001 this was updated by RFC 3066, which added the use of ISO 639-2 three-letter codes, permitted subtags with digits, and adopted the concept of language ranges from HTTP/1.1 to help with matching of language tags. The next revision of the specification came in September 2006 with the publication of RFC 4646 (the main part of the specification) and The current version of the specification, RFC 5646, was published in September 2009. The main purpose of this revision was to incorporate three-letter codes from ISO 639-3 and 639-5 into the Language Subtag Registry, in order to increase the interoperability between ISO 639 and BCP 47.〔(Language Tag Registry Update charter )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IETF language tag」の詳細全文を読む スポンサード リンク
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