I was happy to find a newbb-release for Xoops 2.5.7 in the following modulpack 4.33 RC8:
https://sourceforge.net/p/xoops/svn/HEAD/tree/XoopsModules/modulepacks/x257basicmodulepack/trunk/modules/
But it seems to be incomplete/broken.
After clearing the caches, I was unable to use the forum correctly: klicking on a themes name causes xoops to create a site without any content.
The tips from the German support-forum would have needed a complete upload to be successful.
My way of "repairing" newbb is very strange!
I renamed the modulpath from newbb RC8 and made an ubload of RC13b into /newbb. After a failed actualization of newbb in the modul-install-admin, everything works fine now.

I now need to get complete an actual German translation files. Would be nice, if you could help me.

Greetings
Andy