Restricting search on one language

I know it's a bit late now, but the offline translation is really nice. Only in German, it's a bit complicated, because you also need to update de-formal, but other languages don't have something like this AFAIK.

Dutch and Hungarian also have and (in)formal variant. For Dutch (informal) it has been added to MediaWiki proper, for Hungarian that has not happened yet.

In general, each code has to be seen as indenpendant from any other; when a language has two localisations, that indeed means you have to handle two of them...