Hmm, do you mean names in general or names from the Pokémon TV-show?
If you asked about the show, then I have to say there really isn't any major differences. I mean, Brock is Brock, Ash is Ash and Misty is Misty. In this case, the difference comes from pronouncation: for example, "Squirtle" would be pronounced more like "sqeertleh" instead of the "sque-doh". It's actually quite funny, because the voices of the pokémon are the same as in the English version of the series, so when I was small, I'd keep wondering why almost every pokémon talks by repeating their names but some, like squirtle, didn't. It took me years to realize this was beacuse of the translation. So, the names aren't really that different, it's just that when they're pronounced a bit differently, you can't tell they're the same right away.
And, if you were talking about names in general, which I frankly pretty much doubt, I can give you a great example: my last name is Perheentupa (it means 'family's hut', btw). I can't really explain how it should be pronounced, but not once have I gotten an English-speaker to say it correctly, and I doubt I ever will.
By learning only one language as a kid we really narrow down our potential pronounciation-wise... Many Finnish people speak English in a completely uncomprehensible way because they simply can't say the words correctly, and it annoys the hell out of me. But I guess I'm that way, too, so I don't know if I'm really the one to talk :laugh:
Man, this must be one long visitor message, but it had to be in order to explain this fully. I'm sorry for this being so long, but hey, you asked!