I tried your german.ldf file, and nothing wrong happened in the Quest interpreter. I only used basic commands, and the test game was in english, but what was the problem for you exactly ? When did it happened ? (for which command)
Maybe it's related to your MSwindows version / OS ? Mine is Win98SE, using a Amd K6/2 30 Mhz, and 200 Mb ram.
You can try my french version at :
http://anamnese.online.fr/if/quest.html