Thanks a lot for the offer!
The extension is available here: http://ifiction.pageturner.de/inform7/, specifically http://ifiction.pageturner.de/inform7/German.i7x.
If you have the time and want to take a look, that would be cool. However, to avoid duplicate work, you could try to coordinate the effort with @Mikawa and @ChristianB. As far as I know, they have not abandoned the development, but rather put it on hold, because there was no satisfying solution for various problems which occurred due to internal changes with the Preform layer in Inform.
First, there was a problem in the transition from 6G60 to 6L02, which some translations tried to work around (cf. this thread, but you know more details about that than I do), and then again in the move from 6L02/6L38 to 6M62, cf. this thread.
And the consensus among the developers of GerX was that the most sensible course was to wait until these issues were resolved. That’s the status quo as far as I know.