Are ‘Do you speak English?’ and ‘Can you speak English?’ interchangeable?
to speak English Vocabulary play the main role…
Strictly speaking, “can” asks about ability, and “do” askes about general habit/behaviour, but in practice “do” has developed as a polite way of asking about ability, and is the more usual form when asking a stranger, for instance.
In other contexts there is a difference in meaning. For example, “Do you speak English at work?” (customary behaviour) versus “Can you speak English at work?” (permission/possibility).