It's actually sort of an intuitive idea, as A Ding World points out. There are already games out there that have some sort of imbedded language mechanic built into the game. There's the language of the V'rix in Earth & Beyond, or the simple utility of the Logos language in Tabula Rasa. While it's debatable whether most players pay attention to these instructive nuggets within the game, it seems plainly obvious that the work/reward mechanic of an MMO would have some utility that high school Spanish teachers would have a hard time competing with. If studying had the same rewards grinding did, we might all be bi-lingual by now.