Bad text rendering of Khmer Unicode in Ubuntu

After I installed Khmer Unicode Keyboard and fonts in Ubuntu 9.10, I found some wovels such as ោះ , េះ.... incorrectly display when I typed with consonants.
In this case, just follow this instruction to fix that :

• Open file "enviroment", /etc/enviroment

• Add this line : GTK_IM_MODULE="xim"

example
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games"
GTK_IM_MODULE="xim"

• Save and exit
  

It should work.

Related Documents at Amazon.com :
A Practical Guide to Ubuntu Linux (Versions 8.10 and 8.04)
Ubuntu Unleashed 2010 Edition: Covering 9.10 and 10.4
Beginning Ubuntu Linux, Fourth Edition 
Official Ubuntu Book, The (4th Edition)