blog: bcp47: discuss overlong iso639 #23
Description
https://www.ietf.org/rfc/bcp/bcp47.html
§2.1 Syntax language
"shortest ISO 639 code”
§2.2.1 Primary Language subtag
When languages have both an ISO 639-1 two-character code and a three-
character code (assigned by ISO 639-2, ISO 639-3, or ISO 639-5), only
the ISO 639-1 two-character code is defined in the IANA registry.
§2.2.4.3.d
UN numeric codes for countries or areas for which there is an
associated ISO 3166-1 alpha-2 code in the registry MUST NOT
be entered into the registry and MUST NOT be used to form
language tags. Note that the ISO 3166-based subtag in the
registry MUST actually be associated with the UN M.49 code in
question.
example eng-US is invalid, as is en-840 or en-USA