I think that you have to make an OSK of your language yourself.
In other words, you have to create your own "skin".
The OSK is an image (like other menus). If you use the "classic" skin, you can find all these images in C:\DestinatorApps\Frontend\Skins\Classic.
You have to modify these images with a program (the simplest is "paint"). Erase carefully the letters on each key, and add your own. Thats what i did.
But be carefull not to change the image's dimension. If you do this, you have to modify the .ini in the skin, too.