Thanks from Kindle owners!
I just noticed today that Duolingo is now available on the Amazon Android marketplace. I've been waiting for this, thank you!
You may already be aware of this, but people are rating the app one star on Amazon.de because learning English from German is not available. Your app description is a bit misleading. The same is happening on the Google Play Store as well. I don't know if it's possible to add different descriptions for different countries, but you might want to add a line in German explaining that German is not yet available as a base language.