I uninstalled the default PlayOnLinux and deleted its folders from my home directory as it had a really bothersome bug. I tried to use the compressed version and it had the same bug as in the default one. I tried the GitHub version afterwards and the bug was gone, but there were no fonts, only little black boxes.
Now it seems like that my system is cursed. Every PlayOnLinux version I attempt to run (except for the experimental v5 which is in a state of mess) has no fonts, no matter whether I use the packaged or the TGZ version. Even typing in the drive name yields black boxes... even for Latin characters.
How can I get PlayOnLinux to display fonts?
I managed to solve the problem. The curse was actually a GTK misconfiguration.