Fix wrong (Khmer unicode or other languages) font display problem after installing fonts on Linux

Описание: Check what font is being used now:
fc-match :lang=km

Make font config file and folder if not already existed:
mkdir -p ~/.config/fontconfig
nano ~/.config/fontconfig/fonts.conf

You can find the huge chunk of thing I just pasted here:
https://pastebin.com/FrDg44JP

'ctrl x 'and then 'y' or 'enter' to save changes in nano

Rebuild your font cache:
fc-cache -fv

And then reboot your system