Well, I defined them Slovaks because they are from Slovakia and speak Slovak. I'm referring to those in Folkestone Road, which is the area the questions related to.
As I can understand Serbian, and generally can tell the difference between different Slavic languages, I'm pretty sure I didn't give the wrong information there.
So it wasn't any form of generalisation cliche on my part.
As for speaking-not speaking English, I have never heard them speak English, so I assumed they can't, but perhaps they do, I don't know.