this feature reportedly was introduced in the latest update, i havent tried it out yet so cant tell you how its done. however i once downloaded haypi from the german itunes store and everything in the game aside from wc was in deutsch
It depends on what type of device you're using. If you are using an iDevice (pod, phone, pad) you go to Settings-->General-->International-->Language (I don't know if this is how you change the language but assuming Zate is right that should work)