I was using xdg-ninja to clean up my home folder. But the tool said that $XDG_DATA_HOME, $XDG_CONFIG_HOME, $XDG_STATE_HOME and $XDG_CACHE_HOME aren’t set. And I don’t know where to set them.
Hm. I just noticed this might not work as .pam_environment seemingly might been disabled because of security concerns.
I set them in a file: /etc/profile.d/xdg_vars.sh and now it works, so no worries. I guess this issue can be closed then.