Maybe common, after years of isolation (and the tainted races mixing, and being all a bit on the growling persuassion, with orcs and the such around) becomes so changed that now it's not understandable by the rest of the basin. Harsh sounds, not exactly like growling (loboshiaru or aslaran) and a lot of slang.

If a mechanism were in place to learn languages, which is the only thing that makes sense, then most races would get common and their language, but Viscanti would get common and a free slot to learn one other racial language at no cost.