Nabble is ready to receive new translations and reach more users world-wide. We have a sub-forum dedicated to translations here:
http://nabble-support.1.n2.nabble.com/Nabble-Translations-f6669344.html
Please read the pinned topics if you want to help with translations. And thanks for all the help!
EDIT: If you want to change the language of your app, just open "Options > Application > Change language".