Sorry for being quiet for few weeks,
Okey, please bear in mind that DAP-News and Kohsantepheap are using the Limon S1 font not Khmer OS (khmer unicode).
As you've mentioned that you can mount R/W then it's meaning that your device is rooted
Ok let try this again.
Download this font, extract and copy to your device.
Using Root Explorer to delete DroidSansArabic & DroidSansThai from /system/fonts (make sure you mount R/W)
Go to the font folder that you have downloaded and copy one by one DroidSansArabic & DroidSansThai to /system/fonts
Download Mozilla firefox from the market then reboot your tab. Done.
I have done this many time with my tab (Froyo 2.2) and few of my friends' tab, HTC Legend and Samsung Galaxy S also no issue.
Now I am searching to root my Nexus S GingerBread #2.3.4#
You can call #+855 #0#88 868 8668# me friends if you still fail.