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. Components of language tags are drawn from
ISO 639,
ISO 15924,
ISO 3166-1, and
UN M.49.