Fonts not Showing in Snap Packaged Software

Problem:

You've installed the latest snap package of an application you've been dying to try and are happy to see it published in the Snap Store. But when you launch it, it only shows big hollow squares where it should be showing text. Also the icon spacing might be all wrong.

Solution:

Open a terminal and type:

$ fc-cache -r

This regenerates the font cache.

Result:

No more hollow rectangles for text in your shiny new snap apps.

Thanks to this post on the Manjaro Forum for the answer.