There is also an Accept-Language header line in HTTP2 spec:
http://www0.cern.ch/hypertext/WWW/Protocols/HTTP/HTRQ_Headers.html#z12
Accept-Language:
Similar to Accept, but lists the Language values which are preferable
in the response. A response in an unspecifies language is not illegal.
See also: Language.
Language coding TBS. (ISO standard xxxx)
Content-Language: code
The language code is the ISO code for the language in which
the document is written. If the language is not known, this
field should be omitted of course .
The language code is an ISO 3316 language code with an
optional ISO639 country code to specify a national variant.
Example
Language: en_UK
means that the content of the message is in British English,
while
Language: en
means that the language is English in one of its forms.
(@@ If a document is in more than one language, for
example requires both Greek Latin and French to be
understood, should this be representable?)
See also: Accept-Language.
-- Cheers, Ari --