In 2014 I wrote an steam guide, how to patch Jedi Knight 1 into german language:
http://steamcommunity.com/sharedfiles/filedetails/?id=342794531

The fan-translation includes subtitles for the cutscenes. It also translates the menus and mission briefings (loading screens).
But there is no dubbing (voice acting) and no subtitles for ingame speech. Both are still in english.

Note, that you have to use an unpatched retail 1.0 Exe from Jedi Knight / MotS for patching.
For steam users you have to get this exe from here: http://steamcommunity.com//sharedfiles/filedetails/?id=231648643
I don't know if it works for GoG Version, but it should!
If the game is successfully translated into german, then JK1 / MotS is automatically patched with the latest Lucas Arts Patch. After that you will be able to install the unofficial patches. They should work.

I mentioned there also, that I will create in the future a "steam-guide", with all mission briefings in german.
This hasn't happened yet, but is still planned. It's not only planned for german language, it will be also for english, french, spanish and italian gamers avaible. The problem with the mission briefings is, that JK1 loads too fast on nowadays systems, so you can't read the instructions for each mission.

The Link to the unpatched .exe files is dead and the patcher will not recognize the GOG version.

The link can't be dead, I used it today again on Steam JK1.

Here is the direct link, which was posted on reddit, mentoined in the above steam guide: http://dl.dropbox.com/u/1656336/JKSteamFix.zip

You are correct. The Link was not dead but it was wrong. If you highlight the link in Steam with the mouse you will see that the final "'"' is highlghted, too - that is why just clicking on the hyperlink won't work. Other question: do you also have a copy of the original MOTS executable for the German patch?