"I can only speak English."
We had 会 only as future up to that point. It can mean "having the skill to" too as seen here.
Is 說／说 here necessary?
I know I've heard people asking me "你會中文嗎？／你会中文吗？"
我只能说英文。I have found that the use of "能“ (instead of 会) in this case works as well.
(But Duolingo considers it as incorrect as of right now.)
i have too many lingots... reply to my comment if you want lingots with how much you want (must be 5 or under)