I know we have users from quite a wide variety of locations. Would this be something that they would find helpful (and which might draw in more new users)?
We could probably crowdsource the translations (if we were to use the gettext library, of which there is a PHP implementation, we could pass the .pot files to volunteers for a given language, and have them do the translations at their leisure). I, for one, would be happy to do some French translations.
Then, as languages are added, there could be an option under 'settings' to change your language.
Translating all the documentation and news (and keeping them up to date) would be pretty daunting, but internationalizing the card text would be the most important thing, and that wouldn't be hard at all. A majority of cards use a small vocabulary of words that get repeated a lot ('tower', 'wall', 'attack', 'if', 'enemy', 'stock', etc.).
Would this be more trouble than it's worth? Just a random thought.