ubuntu snap apps lacking proper fonts

 https://askubuntu.com/questions/1224125/font-characters-displayed-as-squares-in-ubuntu-18-04

rm -rf ~/.cache/fontconfig 
sudo fc-cache -r -v 

Delete every found fontconfig folder from the snap cache, e.g. 

find ~/snap/chromium/ -name 'fontconfig'

rm -rf ~/snap/chromium/common/.cache/fontconfig/