I thought I'd already made a ticket for this, but it seems I haven't.
I think it would be nice if works had a language attribute corresponding to the lyrics language. It would let us do several things:
1. For "X is a translated version of Y", we would know the source and target languages and in theory we could display that when showing that relationship.
2. Picard could enter correct data in the TLAN frame, instead of assuming the tracklist language is the same as the lyrics language.
3. We could use the code zxx ("No linguistic content") to mark works with no lyrics, i.e. instrumentals. (this doesn't give us a way to say something is an instrumental performance of a work that normally has lyrics, but it's a start).