Thank you for this great idea, Jeremy.
Presently, Amara filters only allow the search for one subtitle language. But others have already made suggestions to refine them, so watch out for possible changes in the next revision of the interface.
Does this limitation also apply to the API? Also any idea of a timeline for the next interface?
Sorry: I don't know the answer to either question. Maybe you could create a ticket? Tickets go to tech staff who will be able to reply to you.