In Linux, Debian. Blender 2.91.0 alpha (from blender.org)
Most normal (low) chars, and other latin-related, work fine.
Higher up glyphs and symbols aren't working (although I'm not sure if the unicode value is the problem).
- I found the issue when trying to use unicode arrows, which are included in the fonts I tested. I've pasted into Edit mode as well as into the Text Editor and converted to an object.
- Conversion to a text object seems to silently fail. The created Text object is selectable in the Outliner but not visible in the 3d viewport.
Here's the object when created from the Text Editor -- visible in outliner but not found in the viewport:
[Edit] I just tested in Windows 10, with 2.90.0 alpha. Has strange issues.
(I used the Liberation Serif font directly from the windows\fonts\ dir.
I tested Liberation Serif in LibreOffice Writer (but I don't know if they include their own).)
Here you can see the very-complete font in LibreOffice Writer, but a strange sparse display of otherwise-sequential unicode chars in blender: