Many people like to bitch about how Koslov or Khali or even Rusev were wasted by being billed as the monster evil foreigner. But some guys DID work out quite well. They don't have to be an actual non-American (keep in mind Santino is from Canada but billed from Italy (and at one point Russia.) I wouldn't count any UK or Canadian wrestlers as foreign because they rarely have that as a gimmick. But there are some great ones that did work.
My answer would be Tajiri. Dude wais awesome. Great athlete with good charisma but they sure played up that he was Japanese. That was pretty much his gimmick.
Eddie is another. While usually billed from Texas he was from right on the border and they heavily played off the tricky Mexican gimmick for him.