A language of the intellectual content of the resource.
http://www.w3.org/2000/01/rdf-schema#isDefinedBy
http://purl.org/dc/elements/1.1/
http://purl.org/dc/elements/1.1/description
Recommended best practice is to use RFC 3066 [RFC3066],
which, in conjunction with ISO 639 [ISO639], defines two-
and three-letter primary language tags with optional
subtags. Examples include "en" or "eng" for English,
"akk" for Akkadian, and "en-GB" for English used in the
United Kingdom.