Maybe you've installed some addons and changed the font of ALMOST everything in the game but there are a few instances of text in the game that you haven't been able to modify?

It turns out that there is a super easy way to change fonts in the game to any font. This is always on of my first steps when creating a UI. I choose a base font that I want to see everywhere, then use addon options to change the fonts of specific UI elements.

Linked below is a wowhead article that clearly explains exactly how to do it. Enjoy!

I use Futura no2 Demi Bold as my main font of choice in game. It's super easy to read and doesn't take up too much space. It also supports all the weird characters so if people have annoying names, you can still read them. This replaces both Friz Quadrata TT and Arial in my folder.

I actually found this font in the ElvUI additional fonts plugin for retail. It's titled ElvUI G there.

Morpheus Replacement

I use Ringbearer as my Morpheus font replacement. It get cut off a bit in-game, but still looks cool. In the picture here it's the titles of the quest and description. I don't really have it anywhere in game except in the quest log here but it looks cool anyways.