from the Kooka FAQ
F: Is Kooka OCR software?
A: No. Kooka just acts as a front end to different OCR engines. Kooka calls external OCR programs or uses libraries.
The first supported OCR program was gocr, which was written by Joerg Schulenburg, but nowadays there are others. It is one of Kooka's design targets to support as many OCR engines as possible.
So since Kooka isn't OCR software to begin with, the answer would have to be, you CAN"T add fonts to it.. you need to look further and see what OCR engine you are actually using. gocr, tesseract, other.
How to Train Tesseract
How to train gocr-- no clue on this one, their documentation is non-existant
How to train ocrupus
How to train GNU Ocrad - again no docs found..