Ok, this is what I’ve gathered:
XDG_CURRENT_DESKTOP is standardized by freedesktop.org. It’s value should be one from this list. In my case, I’ve set it to XFCE via my ~/.profile
export XDG_CURRENT_DESKTOP=XFCE
Neither XDG_SESSION_DESKTOP nor DESKTOP_SESSION are standardized so setting them according to your real session seems best. For example: i3, dk or dwm.
It’s probably best to check their current values by doing echo $DESKTOP_SESSION and/or echo $XDG_SESSION_DESKTOP. If they’re correct, they can be left alone.
More details here.
Those seem to be the only relevant variables for this issue.
This seems like the actual solution 
Thank you very very much for your help @anon93652015 !!