Hi, and thank you for your interest!
OsmAnd is being translated using Weblate, a web tool designed to ease translating for both developers and translators.
Translation project for OsmAnd into Upper Sorbian currently contains 5771 strings for translation and is 18.8% complete.
If you would like to contribute to translation of OsmAnd, you need to register on this server.
Once you have activated your account just proceed to the translation section.