A lot of languages are not in the list we rely on but people will still want to enter them. In oder to allow this we add an additional language code "mis" which can then be used to enter mis-x-Q1234 etc.
GIVEN I am on a Lexeme page
AND I edit the language code of the Lemma as "mis"
AND click save
THEN the input is accepted and the edit saved
- LexemeTermLanguageValidator, currently using ContentLanguages instance)
- (for the language code dropdown on the Special:NewLexeme page): SpecialNewLexeme::getFormFields, and there see: HTMLContentLanguageField (the latter is the "core" Wikibase class with kind of hard-coded use of MediaWikiContentLanguages)