For Mac user, you need to go through the followin.
Download Khmer Unicode for MAC OSX Setting up Khmer Unicode for Mac is different from installing Khmer Unicode on Window. The keyboard layout suggests that the unicode may not be correct, as it verified that the 'f' key shares the same symbol as the 'p' key. I downloaded new fonts to make sure it wasn't just an issue with the font. I am trying to use Khmer unicode and fonts, but for some reason, my 'f' key is showing up as a 'p' key (in Khmer).
Khmer Unicode Keyboard Layout For Mac 5,0/5 8845 reviews
