FTR the issue was an /etc/fonts/fonts.conf
that the fontconfig in the snaps couldn’t understand:
~$ snap run --shell pick-colour-picker
bash-4.4$ LD_LIBRARY_PATH=/snap/gnome-3-28-1804/current/usr/lib/x86_64-linux-gnu/ /snap/gnome-3-28-1804/current/usr/bin/fc-list
Fontconfig warning: "/etc/fonts/fonts.conf", line 5: unknown element "its:rules"
Fontconfig warning: "/etc/fonts/fonts.conf", line 6: unknown element "its:translateRule"
Fontconfig error: "/etc/fonts/fonts.conf", line 6: invalid attribute 'translate'
Fontconfig error: "/etc/fonts/fonts.conf", line 6: invalid attribute 'selector'
Fontconfig error: "/etc/fonts/fonts.conf", line 7: invalid attribute 'xmlns:its'
Fontconfig error: "/etc/fonts/fonts.conf", line 7: invalid attribute 'version'
Fontconfig warning: "/etc/fonts/fonts.conf", line 9: unknown element "description"
Fontconfig error: Cannot load config file from /etc/fonts/fonts.conf
the user’s fonts.conf
had been fiddled with by either fontconfig-infinality
or “fonts tweak tool” [sic]; reinstalling the default fonts.conf
from fedora 30 resolved the issue.
maybe snap authors (or desktop-launch?) can detect and alert the user about this scenario?