Yeah, Fallout is too American to work elsewhere. I'm not saying that as a negative either, I think it's awesome, but it just wouldn't work. The only possible exception would be Canada, but then you might as well just make an Alaskan Fallout setting. Even a Western-European setting would be hard to do well as you couldn't market, say, a French Fallout to an English speaking audience without everyone speaking in phony French accents that would ruin the mood. And an English Fallout would just be totally different.
Well... come to think of it, possibly an Australian Fallout might work best. But still, for me, Fallout is and has to be in America.