My iPad 3 is set to use English as the main language for everything in the settings (International and Keyboard settings).
When I download an app, it's very often in the Russian language (when there's a translation available). And I don't know why. I don't even understand their alphabet so the apps are very unusable.
I already checked my AppStore account - but it's in Czech (that's where I live), which has got a classic alphabet.
Sorry about my English, I'm not a native speaker.