Hi Raphael,
This is something that I want to seriously address with version 2. Unfortunately, right now the translation process is a very time consuming one as it involves going through every single template, digging through the bits of HTML, template tags, and english text and replacing just the english text. All of our products have a similar problem, however Gossamer Forum specifically has an additional problem: markup tags. Because some of them ([email], [url], [image]) are coded into the markup conversion code itself, providing a full translation is a very difficult task - hence the german translation does not have this part translated. The french version does, however, and although it works it was much more work to get it done than it should have been.
I don't want to promise one way or the other on what we're going to do for version 2 yet - we aren't completely sure ourselves - but the language issue is certainly one of the larger issues. In any event, we want to translation interface to become much much easier for translators to work with, so that they will essentially be editing english strings instead of worrying about making the translation fit into the same HTML. My hope is that a much-improved translation system will make the job of our translators much easier, and that will undoubtedly lead to better product translations.
However, for the current version there isn't an easy way to get the german user side with the english admin panel. The easiest way is going to be similar to what you guessed - although you needn't install them both. Just download the english version, and open it up on your computer (with Winzip, Power Archiver, or anything else that understands .tar and .gz files). What you want to do is rename the install.dat file from the english version to install.tar, then open that file with Winzip. That install.dat is actually a tar file, containing all of Gossamer Forum program files, templates, etc. To get the admin templates, you need to get the files in cgi/admin/templates/admin. That will certainly save you the step of installing twice. Not everything will be in english - column names, for example, but just about all of the options and descriptions will be.
Jason Rhinelander
Gossamer Threads jason@gossamer-threads.com