Which of the following sounds correct to you?
AA) Is English your first language? If so, then what dialect do you speak? If not, then what is your first language?
AB) Is English your first language? If so, then what dialect do you speak? If no, then what is your first language?
BA) Is English your first language? If yes, then what dialect do you speak? If not, then what is your first language?
BB) Is English your first language? If yes, then what dialect do you speak? If no, then what is your first language?
As for myself, only AA sounds right.
AA) Is English your first language? If so, then what dialect do you speak? If not, then what is your first language?
AB) Is English your first language? If so, then what dialect do you speak? If no, then what is your first language?
BA) Is English your first language? If yes, then what dialect do you speak? If not, then what is your first language?
BB) Is English your first language? If yes, then what dialect do you speak? If no, then what is your first language?
As for myself, only AA sounds right.