The AIR SDK we used is 1/14/2014 Release - AIR 4.
The device we have tested on is Samsung Galaxy Note 3/Android 4.4.
We found that it's quite similar with Bug 3681788 which has been fixed in Beta version 4.0.0.1619.
We checked the issue again with this beta version, and the result is Chinese characters are shown correctly, but Korean's are still not.
Bug 3681788: The CCJ languages characters are displayed as blank box on the TextField.
Hope it can be fixed as soon as possible.