I've just pushed an update to our locale repo and crowdin to completely remove the translation from the sources, as it's actually not serving any real purpose in this case and only can cause issues if someone tries to translate the variable name.
@Martin you can download a fixed version of the translation file here.
Simply upload it to your FOSSBilling instance and replace the
\locale\de_DE\LC_MESSAGES\messages.mo file with it.
Keep in mind, these translation files are meant to be paired with our development branch for FOSSBilling 0.5.0 and as such it doesn't contain all of the strings for FOSSBilling 0.4.3, so you may see less portions of FOSSBilling being translated, however this should be mostly limited to the administrator panel & primarily in ways you would likely never notice to begin with.