The issue is related to fontconfig's bug (See https://forum.snapcraft.io/t/snapped-app-not-loading-fonts-on-fedora-and-arch/12484/18).
Try the workaround here: https://forum.snapcraft.io/t/snapped-app-not-loading-fonts-on-fedora-and-arch/12484/60
Solution 1.
rm -r ~/snap/snapname/common/.cache/fontconfig
touch ~/snap/snapname/common/.cache/fontconfig
replace snapname with the version of Stacks you have installed in the snap folder
Solution 2.
sudo pacman -S yay
yay -S debtap
sudo debtap -u
debtap stacks-app_[ver]_amd64.deb
sudo pacman -U ./stacks-app-[ver].pkg.tar.zst
