Some photos leaked iOS7 can show font Khmer Unicode in notification. In fact, on iOS7 new features custom font function on iOS7 not yet available for us yet on version 7.0 until 7.0.3.
One way that you can install Khmer font and Khmer keyboard on iOS7 is your device must jailbroken.
But unfortunately, Until now jailbreak team still working on it. They not yet release tools for us to jailbreak our device.
So for user want to read Khmer Unicode on your device, You just can read the news from Khmer browser apps that the developers designed by embed Khmer font in App Store.
iPK Khmer Browser