Why is my gear fit in german?

I recently bought it off someone. Everything was working fine. Once i reset it, everything changed to German. Gave it back to the person & she took it to have it fixed. Once I got it back, it did the exact same thing. The guy that fixed it at best buy used some kind of link on his phone. He's out for the day and now I'm stuck. Anyone know what to do or had this problem?