Play wwf in two different languages with two different people

So I'm playing wwf, which is great. I play it on facebook. I'm a native english speaker, so when I put down words I'll put the english term, say, "WORD".

Right now I'm learning spanish, so i thought it would be fun to play with a spanish-speaking friend, and use spanish words, say "PALABRA".

I don't know how to do this. There is a "gear" icon in the top-right, but that just changes the words used in the GUI to whatever language. It has an indicator below it that would attest that spanish words can be used... but then it won't accept spanish words on the board, only english ones.

I would also like to only change the language settings on a game-by-game (or, better, person-by-person) level. ie I don't want all my games in spanish.

How can I achieve this?