Finally, I found a Multilingual Keyboard input software for Windows Mobile that you can download from XDA-Developer forum for free. It is FingerKeyboard 2.1.
<< if you are looking for Khmer Unicode for Windows Mobile click here >>
There are 4 edition available for FingerKeyboard 2.1
WVGA: for Screen with the size of 800 x 480 (pixel)
WQVGA: for Screen with the size of 400×240 (pixel)
VGA for Screen with the size of 640×480 (pixel)
QVGA for Screen with the size of 320×240 (pixel)
+ Where and How to download?
1. Register at http://forum.xda-developers.com/
2. Browse…