[rdesktop/kde-focal] Unable to change systemsettings

I tried the rdesktop docker Image either kde-focal.

The default user abc is unable to change any system-settings.
I tried to add additional language but the button is grey.

Is there a simple solution to fix this?

P.S. There is no matching Tag for rdesktop

Have you tried running the command with sudo?

I tried running ‚systemsettings5‘ with sudo from terminal, but that didn’t worked.

You did see the banner on top of Language in system settings? It says that there are no additional languages available on this system.
But I don’t know how to install more languages so it shows up in that list.

It‘s not only language settings not working.
Changing the timezone ends with a not authorised message.

I tried installing additional language-packs from the commandline, but they do not appear in the language settings.