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| BCP 47 | |
|---|---|
| Name | BCP 47 |
| Othernames | Best Current Practice 47 |
| Status | Internet Best Current Practice |
| Published | 2006 (RFC 5646), 2010 (RFC 4646), updates |
| Authors | Internet Engineering Task Force, Internet Architecture Board |
BCP 47 BCP 47 is an Internet standards document specifying language tag formation for identifying human languages in protocols and formats used on the Internet. It provides a framework adopted by organizations such as the World Wide Web Consortium, the Internet Engineering Task Force, and the International Organization for Standardization to enable interoperable language identification across software, standards, and content. BCP 47 builds on legacy standards and is widely implemented in browsers, operating systems, and localization toolchains.
BCP 47 unifies several predecessor efforts including RFCs and ISO standards from bodies like ISO/TC 37, Unicode Consortium, IETF working groups, and the World Wide Web Consortium. It interacts with registries curated by the Internet Assigned Numbers Authority and the IANA policy frameworks endorsed by the Internet Architecture Board. Major technology adopters such as Mozilla Foundation, Google LLC, Microsoft Corporation, Apple Inc., and Linux Foundation implement BCP 47 in products including Firefox, Chrome, Windows, macOS, and distributions like Ubuntu.
BCP 47 defines a hierarchical, dash-separated tag syntax influenced by standards from ISO 639, ISO 15924, ISO 3166-1, and IETF language tag practices. Tags combine primary language subtags, script subtags, region subtags, and variant subtags to represent specificity required by applications such as HTML5, XML, HTTP, SMTP, and JSON. Implementation guidance references examples from technologies maintained by W3C, IETF HTTP Working Group, and localization platforms used by Adobe Systems, Oracle Corporation, and SAP SE.
Language subtags derive from sources including ISO 639-1, ISO 639-2, and ISO 639-3 codes; script subtags come from ISO 15924; region subtags use ISO 3166-1 alpha-2 and UN M.49 groupings such as those used by United Nations agencies. The tag registry maintained by IANA maps to entries influenced by linguistic projects like Ethnologue and scholarly resources from institutions such as Linguistic Society of America and SOAS University of London. Examples of language-region-script combinations appear in standards implementations by Mozilla Foundation, Google LLC, and in datasets curated by Wikimedia Foundation.
BCP 47 specifies extension mechanisms, including singleton-prefixed extensions and a private-use subtag, used by platforms like OpenSubtitles, Netflix, YouTube, and content-management systems from WordPress Foundation and Drupal. Extension subtag proposals have been discussed in venues including IETF Working Group meetings, drafts submitted to the Internet Engineering Task Force and coordination with registries such as IANA. Private-use subtags enable vendor-specific tags employed in products by Facebook, Inc., Twitter, Inc., Amazon.com, Inc., and Shopify.
IANA operates the subtag and language-tag registry that enforces policies set by the Internet Engineering Task Force and the Internet Architecture Board. Registration procedures involve expert review and community input similar to processes used by ICANN for DNS policy and by W3C for web standards. Major registered subtags reflect inputs from standards bodies including ISO, the Unicode Consortium, and linguistic authorities such as Summer Institute of Linguistics.
BCP 47 is implemented across operating systems, browsers, and applications: examples include locale negotiation in HTTP/1.1, language negotiation in HTML5 lang attribute, locale APIs in POSIX, and frameworks such as Java (programming language), .NET Framework, and libraries used by Node.js. Content providers like Wikipedia, BBC, The New York Times, and Netflix rely on BCP 47 for delivery of localized resources, and standards such as PDF, SVG, and XLIFF reference BCP 47 for language annotation. Internationalization tooling from organizations like OASIS and W3C Internationalization groups integrates BCP 47 guidance.
BCP 47 interoperates with related standards including RFC 2119 for requirement keywords, RFC 5646 and RFC 4646 historical documents, ISO 639 family, ISO 15924, ISO 3166-1, and character encoding work by the Unicode Consortium as specified in Unicode Standard. Its relationship with web standards produced by the World Wide Web Consortium ensures consistent behavior in HTML, CSS, and XML processing across implementations by companies such as Google LLC, Mozilla Foundation, Apple Inc., and Microsoft Corporation.
Category:Internet standards