Cristina Aguilera's parents divorced when she was very young and she was reared by her mother, a Yankee, in Pittsburgh. She didn't really have an opportunity to learn Spanish.

Other 'cross-overs':

Selena didn't speak any Spanish either, but had she not made albums in Spanish she certainly wouldn't have become as famous as she did, since she didn't get anywhere with her intial foray into American pop.

Linda Rondstat - she has a beautiful voice for mariachi, but a few Spanish lessons wouldn't hurt.

And Shakira is from Colombia, but her father is arabe.