Do you speak english?
This question is more complicated them one can imagine.
Not the question itself, but the essence of the answer, cause who`s going to answer, makes other questions like:
Do I speak English fluently?
Is this person trying to cheat me, or test me?
Do I have enough vocabulary?
Most of people are afraid of speaking English, what just makes things worse, cause this feeling will just make this person not to practice. It also seems that people are always competing each other to have more information, to be more intelligent, or to speak better an idiom.
Even among teachers this thinking comes, but it should not be so, try and use your knowledge the way you know, mainly for students. The mistakes is part of the learning process. Let`s speak, lets talk, and during this process we learn together, we teach each other.
So when anyone ask you if you speak english or not, just say yes! and go on aboard.
But please I beg you don`t you hunt Strangers, its not positive, next time we talk about it.