1- first all you need to Root your phone in flashtool

2- and after that you install File manager from Google play then go Setting of File manager  check box on Root Explorer and Mount System Folders

 

3-  You click UP till see /

4- then you fine folder System then Font and past your font here

5- and you need copy font Khmer to your SD card
6- then you copy font khmer to past in System/fonts

7- Enjoy !!!

Warning: your phone may error and lost your System...