I didnt know everyone assumes he is german. since in America they have surnames from all over Europe.
So a german surname doesnt stop him from being American.
Considering he spoke ENGLISH in the anime, I assumed he was American.
Since there is no deeper info's I guess it remains unkown where he is from. I dont see how it is safer to call an English speaker German but whatever.

Anyway, on the subject of education, English is usually taught in Germany starting 4th grade (as far as I know at least, they might have changed it in the last few years), and as those guys might have been from all over the world (which is what their surnames suggest), it would be quite natural for them to speak English.
What might be considered a point against all of them being American is that they were called foreigners instead, I'm really grasping at straws here though.
So yeah, we don't actually know where he comes from.