I think it makes the most economic sense for there to be specialized relays specifically language specific relays, but there's nothing keeping both from existing (except that maybe nonspecialized relays might go broke or switch to being paid services but I think we're moving towards paid relays or friend hosted relays either way)
Discussion
yes, hard to know what the future relay landscape will look like. I do agree that languages specific relays will be a thing. I also agree that people would likely want translation relays and such.
all i'm saying is language query filter is first step and good short term solution to jump start language specific feeds.