From first grade until university, I studied Spanish... and since I moved to Japan, I have forgotten it all. Kaput, gone, bye-bye. But not Mario voice actor Charles Martinet. He totally remembers it.
At a recent presentation, Martinet not only showed his Mario voice acting skills, but his mastery of the Spanish language. Since Mario speaks English on the recent Japanese versions of Super Mario Bros, I'd imagine that the same holds true for Spanish versions of the game, too.