Language range search

[nichtich]

Language ranges may be complex to implement, so it might become an optional extension.

• prefLabel=x (any language - requires another schema in MongoDB!)
• prefLabel.en=x (only en - easy to implement in MongoDB)
• prefLabel.en-=x (language range, e.g. en, en-US, en-GB... - ?)

[nichtich]

There should also be special request parameter language to override Accept-Language