Install xfonts-thai by entering the following commands in the terminal:
sudo apt update sudo apt install xfonts-thai
Description:
Collection of Thai fonts for X (metapackage)
This is a metapackage which depends on or recommends all available Thai fonts packages.
Homepage: https://linux.thai.net/projects/thaixfonts
Version: 1:1.2.7-3
Section: universe/x11