Thanks. It is the eu sound I have problems with. The wikipaedia site suggested that eʊ̯ is like ceux in French, which makes it a lot clearer. (Although the wiki on Czech said it is like the eu in pneumatic, which definitely didn't help!)
Eu is pretty weird, yes. Some other French vowels are weird too, notably all the nasalized ones. But, as I said to Callaina recently, I think English has more vowels than French, and therefore more weird ones too — that is, vowels that will sound weird to people whose native languages have a much smaller variety of vowels.
There's a fair amount of weirdness in the impurity of the vowels, which is why an anglophone accent is often easy to recognise in other languages. But that's only standard English; as you've heard, there are dialects with pure ones.
Edit: that's misleading, I suppose, since there are some pretty impure vowels in some dialects. But you probably know what I mean.