You know how, in English, we sometimes say "It's Greek to me" when we find something incomprehensible? There's a similar idiom in Greek, but they reference Arabic as the quintessentially incomprehensible tongue. And Arabic speakers say something incomprehensible "sounds like Hindi." Talk about cultural relativism. Here's a map (from Language Log).
Generally speaking, Chinese is the clear favorite for most stereotypically confounding language. Although Mandarin might be taught more in schools around the world in the coming years.Via Eyeteeth.