Font problem: Boxes instead of characters in some applications
 

Hello, I'm dealing with a very annoying problem: Since a recent fresh install of Archlinux, I have a problem with fonts in some applications. Some areas that should show legends/labels of functions, show boxes with letters and/or numbers in them. This happened in Audacity and Cecilia so far (see attachments) and I'd rather see the problem fixed than avoiding the applications that have them. I'm using Archlinux with realtime kernel (RT-Linux 5.4) and some applications necessary for my requirements, including said affected applications. I have installed a few fonts recently that I use for my desktop along with pscircle as part of my desktop background. Did I mess something up? If yes, what could it be?

What desktop environment are you using?

I knew I forgot something lol, I'm using TWM. The thing is I never had any problems with this setup, so I wonder if there is a font that used to be a dependency for Xorg or TWM, but isn't anymore?

Only those two?
I cannot find Cecilia in the repos or AUR.
It could well be application specific - Audacity uses wx-widgets, I've had (minor) problems with it too.
Try reinstalling audacity & its dependencies.
If no fix, start audacity from terminal. Scrutinize output.

https://wiki.archlinux.org/index.php/Font_Configuration

How about this?
audacity depends on gtk3, which depends on pango
https://gitlab.gnome.org/GNOME/pango/issues/386
https://bugs.archlinux.org/task/63297