We're not yet sure what's involved in adding languages to the app, particularly when those languages require significant design changes (like Japanese, for instance). So for the moment, we're going to avoid giving out defined timelines until we can be sure about them.
Be aware that we're doing our best to get everyone's languages out as rapidly as possible. Gabe, in particular, is champing at the bit to use this app for his own Japanese (and Japanese is one of the last releases), and we have a lot of financial incentives to release languages rapidly, as well. (Note that your subscriptions don't actually start until you're learning your target language).
So rest assured that there's lots and lots of incentive for us to move quickly!