Just some ideas...

I was thinking of a game that would teach you another language. The setting could be that you get stranded in a different country (maybe because of a quarantine) and you have to join forces with some of the natives to survive the disaster. In the lower levels the NPC's will speak mostly English. But as the levels progress you have to start speaking and understanding more of the other language, maybe Spanish. Or you could select the other language you would like to learn at the start of the game. Or you could base the amount of English the NPC based on that characters importance. So the doctor at the end of the game who knows the cure speaks only Spanish, or specified language. Where the first person you meet, to point you in the right direction, speaks 95% English.