On Wed, May 25, 2022 at 2:14 AM Samuel Sieb samuel@sieb.net wrote:
A font viewer should only use the system font folders and any modern font viewer will use fontconfig, which won't be looking in random directories.
The fontconfig system has a well defined way to configure the directories it searches, see "man 5 fonts.conf". I would not be surprised to find that some applications add "random" entries to the fonts.conf directories. There are also ways to specify a user font directory. Some linux distros provide this "out of the iso".
The font conf files can define "aliases" so that a document that requests a given font may use a "similar" substitute. This generally works for legacy documents in Western languages, but there have been instances of people adding new glyphs to support for other languages without changing the name of the font.