Just wanted to clear that up from the "let's speak some spanish" thread AND he can speak it a bit but he's not good at it so he doesn't use English. So the only reason you'd have to learn Spanish is to understand what HE'S saying, cuz he can understand what you're saying...mostly...like 90%.
If you see his interview video from several tournaments, you can see he understands English 90% (or more) like Guille's girl said. He didn't have to wait for the translator to translate questions from English to Spanish before answering them (in Spanish, that is). So I'm sure he understands English. Just don't speak too fast when you get a chance to talk to him!