Gothic 2 NotR versions:
You need the so-called Report Version of Gothic 2. But note: Due to incompatible naming conventions you will probably have no sound and no subtitles in your original Gothic 2 after installing this patch. To fix this problem do the following:
The modification itself:
German voice output
To hear German voices in the Game download Velaya_Speech.exe (German).
If you speak German, make sure to check out the German page for more downloads.