Translation:What does he say?
That's an interesting, logical question, but to say "What language does he speak?" I would probably try 他说什么文? or 他说哪文? or 他说哪一个文? (for this last one, I have used the "generic" numerary adjunct 个, as I do not know any count particle specific to languages). My attempts here might be incorrect, but I do think they would at least be understood.