TubMUD is a lib which appears to be popular with speakers of the German language.
Known official links and online resources are scarce/broken. Please feel free to add TubMUD information to this thread as you find it.
From the LPMuds FAQ:
Very intricate, and, according to Rust, "it is beautiful if you
can figure it out." Intended more for Tub wizards to run at
home than for wide-release.
Runs under: LPMud 3.2 (native)