App Store is the wrong language

Solution 1:

Open Settings and go to Store. From there, choose Sign Out if you're already signed in and then sign back in again. If you were not signed in, sign in now. Now check the App Store. If necessary, restart the device.

Solution 2:

I had the same problem (stuck in German store/language). I called Apple support, reset the iPhone, logged into the store, switched to (in my case) my "home" store, the USA. I then restarted the phone and the settings stayed in USA/English.

To reset go to: Settings > General > Reset > Reset all Settings. This doesn't affect your data; just wipes the preferences.