In order to implement the spelling variant field we need to retrieve the list of language codes from WikibaseLexeme.
Note: the list of language codes for the selector is currently coming from Wikibase Lexeme Term languages i.e. mediawiki + additional hardcoded Lexeme language codes. For this ticket we will just use the Wikibase Lexeme Term languages as the initial set of language codes. We will expand/change that in a later ticket.