1. The bass response is not good. Apparently frequencies in the lower range will be (I guess less than 100 Hz) cut off or not transferred. For language is no problem, music is something flat.
2. In my copy two French but no German instruction totaled. Since I unfortunately can not name any links or URLs here, the following notice: The homepage of the brand "call STEL" (if in doubt seek search engine) for the item number "HZ-2037-91" (not mentioned in the Amazon product description) are looking for. There's the Manual and the Quick Start Guide in German (PDF).