I loved Kelly on World Idol, but this is the performance I keep watching over and over again!
In the American votes Diana placed 3rd, so I don't really think, at least here in the states, that the language barrier was an issue. In fact, it's what made this performance stand out from all the others.
Good music is good music, and like others have said: the whole world DOESN'T speak English.
I think it would've been better if they had 'all' had sung in their native tongues.