会, as a verb, has a lot of meanings. You could interpret 'be able to' in your context.
Usually, you'd better add a verb after 会 for this usage in order to be more clear. For example, 我会跳舞（I'm able to dance）；我会手机 is unnatural and vague, it doesn't tell what you are able to do with 手机. So, you could put 我会玩手机，我会使用手机.
As in your example, "你会英文吗？"; it doesn't tell whether you 会（be able to） speak or write. People have to guess what you mean according to the context. In order to be more clear, you'd better put "你会讲英文吗？" or "你会写英文吗？".
In short, when 会 is used as "be able to", you should put a verb or verb phrase as its target in order to be clear.
As for 你说英文吗？, it's kind of a vague question too. It could mean either "are you able to speak English" or "Do you want to speak English" according to the context. So, in order to be more clear, you could put "你会说英文吗？"(are you able to speak English) or "你要 用/讲 英文吗？"(do you want to speak English.).