This is not a duplicate of Mathematica versions 10 and 11 fonts are broken on Linux. There the issue is with PDF export and printing.
The fonts in Mathematica on my system are all messed up, see the Screenshots below. I think I have installed the
mathematica-fonts packages on my Debian GNU/Linux stable system but this did not resolve it.
It seems as if the only subset working properly is ASCII.
A websearch brought up a thread on the Arch Linux forum: https://bbs.archlinux.org/viewtopic.php?id=184112
The suggestion there is to disable antialiasing for fonts in the KDE control center and removing
~/.config/Trolltech.conf. I didn't have the KDE control center (I don't use KDE) so I installed it and followed the steps but to no avail.