The idea sounds great, but the app description definitely should have mentioned what languages are available. I spent five minutes fighting with the faulty OAuth only to find that German is not offered.
I'm looking to support German the first half of this year. It's currently number 2 or 3 on my new language priority list. If you'd like to get an email when it's available, there is a form at the bottom of the homepage that let's you fill out what language pairs you're interested in.
Looks like a great app; while I'm learning german I will definitely sign up when it becomes available.