Here is the thread which discusses how to convert the .vkb files. I'm going to test it out myself later this week. It seems this was tested in the Chinook days, so how well it works for Diablo remains to be seen.

I just figure it might be easier to theme the existing keyboard rather than replace it, especially considering how often it has been tried in the past.

Now if only this script could be used to extract the theme of Opera's keyboard.