Why there are only the English version on GOG, I can remember, that XvT also had a german version

I've provided Judas with the German version. Everything else is up to Disney and GOG.

If German versions exist then it would be really great to see them added to gog.

If you have the original German CDs, you can simply replace the English speech and string-files on the GoG-Installation with the German ones from the CDs.
(Works with X-Wing CD as well)