Language Identifiers in the Markup Context HTML

HTML

See "Language Tagging in HTML and XML."
By Martin J. Dürst, W3C i18n Coordinator.

"Language codes as defined in RFC 3066 can be (and should be) used to indicate the language of text in HTML and XML documents. For HTML 4, language codes are specified with the lang attribute. For XML, language codes are given in the xml:lang attribute. In both cases, language information is inherited along the document hierarchy,i.e., it has to be given only once if the whole document is in one language, and language information nests, i.e., inner attributes overwrite outer attributes... Language codes starting with i- are defined in the IANA registry of language codes. Language codes starting with x- denote experimental codes without guarantee for uniqueness... Many other W3C and Web-related specifications use language codes [for example], (1) XHTML 1.0, reformulating HTML in terms of XML, which advises to use both the HTML lang attribute and the XML xml:lang attribute, with the later taking precedence in case there should be any differences. (2) HTTP uses language codes in the Accept-Language and Content-Language headers. (3) SMIL and SVG can use language codes in the statement. (4) CSS and XSL use language codes for detailed style control..."

On HTTP, see Hypertext Transfer Protocol -- HTTP/1.1 = IETF RFC 2616. From Section 3.10 'Language Tags': "A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language [14.4] and Content- Language[14.12] fields. The syntax and registry of HTTP language tags is the same as that defined by RFC 1766. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags: language-tag = primary-tag *( "-" subtag ) // primary-tag = 1*8ALPHA // subtag = 1*8ALPHA. White space is not allowed within the tag and all tags are case-insensitive. The name space of language tags is administered by the IANA. Example tags include: en, en-US, en-cockney, i-cherokee, x-pig-latin where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 country code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered in future.)"