So I was looking at this answer on stackoverflow and realized that my fonts aren't covering a whole lot of the utf-8 unicode spectrum (as I get lots of squares). Does anyone know a font that will cover all of that post?
The hands-down most comprehensive coverage would be Roman Czyborra's GNU Unicode Font project. It is intended to collect a complete and free 8×16/16×16 pixel Unicode font. It currently covers 34,445 characters (out of ~40,000+ defined characters).
Most distributions have GNU Unifont in their repositories.
Ed Trager has written a Unicode Font Guide For Free/Libre Open Source Operating Systems which collates geographic coverage of fonts and their associated licensing. The guide was last updated in 2008.
Other fonts with good Unicode support include:
I came across this in 2016.
A single TTF/OTF font is never going to cover all utf-8 characters. There is a hard limit of 65535 glyphs in a font, and over 1 million utf-8 glphys. You will need to use a font-family for this to work.
A good font-family is the noto font family: https://www.google.com/get/noto/