I tested using Xubuntu 18.04 Live ISO. The default ISO is configured with en_US.UTF-8 UTF-8.
Generally, I test with various Ubuntu based distros (Xubuntu, Lubuntu, etc.) and they all come preset with UTF-8 "out of the box."
You has mentioned "I wouldn't consider it a 'clean install'", so perhaps something changed on your system after your initial install?
Hopefully this will resolve your problem.
I tested using Xubuntu 18.04 Live ISO.
The default ISO is configured with en_US.UTF-8 UTF-8.
Generally, I test with various Ubuntu based distros (Xubuntu, Lubuntu, etc.) and they all come preset with UTF-8 "out of the box."
You has mentioned "I wouldn't consider it a 'clean install'", so perhaps something changed on your system after your initial install?
Hopefully this will resolve your problem.