As an RDF consumer (linked data interface, query service, or dumps), I want to work with standard language codes, not custom MediaWiki ones.

Problem:
We currently directly export the internal language codes to RDF (in terms and monolingual text): simple instead of en-simple, de-formal instead of de-x-formal, etc.

Note that we do map the language codes already for sitelinks (schema:inLanguage, schema:name).

Example:
The sandbox item currently has a label in “de-formal”; to this query, that should appear as “de-x-formal”, but currently it doesn’t.

Screenshots/mockups:

BDD
GIVEN
AND
WHEN
AND
THEN
AND

Acceptance criteria:

• the language tag of labels, descriptions and aliases uses standard language codes
• the language tag of monolingual text values uses standard language codes
• the language tag of the schema:name of a sitelink uses standard language codes (already the case, should not regress)
• the schema:inLanguage of a sitelink uses standard language codes (already the case, should not regress)

Open questions: