Some Gnome applications (Claws Mail and Glade in my case) show
rectangles in place of characters. Screenshot of this is attached.
Terminal logs in these cases show for example:

(claws-mail:14616): Pango-WARNING **: 12:31:34.945: shaping failure,
expect ugly output. shape-engine='PangoFcShapeEngine', font='Cantarell
Oblique 11', text='Personal'

I've tried manually installing 'font-abattis-cantarell' into my
profile, which did not solve this problem.