What is the difference between the characters 会 (huì) and 说 (shuō), for example in these simple closed questions:
你会英文吗？ [Nǐ huì Yīngwén ma?]
你说英文吗？ [Nǐ shuō Yīngwén ma?]
I am wondering since various online resources give both of them as examples of the verb 'to speak' or 'to say' but I want clarification on whether this is correct and if there are any rules on when to use them in different contexts.
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.).
This is exactly what I stuck in at the very early stage of learning Mandarin!
会 is usually used as an auxiliary verb (mean "can", "will", etc...) and thus take a verb after that, but it can also function as a verb, to mean "know" or "understand".
That's why in your example, both mean "Do you speak English?".
Also, if you want to use 会 as an auxiliary verb, you can also say "你会说英语吗？".
In spoken language, 吗 at the end and with a rising tone , in most cases, represents a question. Without 吗 at the end but in a rising tone, also is a question. No big difference. But it sounds natural and better with 吗 but not necessary when you ask a question.
Under some particular circumstance, 吗 at the end, read in a little prolonged way, can mean something different. Like a daughter who is pestering her Daddy to buy her some candy might say "爸爸, 给我买些糖吗, 恩, 求求你了吗. "
There might be other special uses. They have not crossed my mind at the moment.
Hope you like my answer.
