You’re talking about
de-de but your screenshot shows
en-us which has no translations yet.
You have to translate these - see: Knowledge Base — Zammad (for Agents) documentation
I get the point that the entries are not translated.
But no matter which language i chose, all Knowledge Base entries are gone. Even in the standard language we used they are not showing up…
You may be lucky by running
zammad run rails r "Cache.clear" if you’re on a package installation.
Hard to tell as you didn’t provide that information.
While we’re at that, please upgrade to Zammad 5.1 as 5.0 is prune to security issues.