Change or edit dictionary file

As most people know it's possible to save one's dictionary in a backup. The file is of the type *.u20. I couldn't find anything on the net about this extension. Does anyone know how to edit of substitute this file? My plan is to change this file to a german dictionary, but I haven't got a clue how to do it yet...

maybe open it with notepad, maybe the language in the file is readable

First thing I tried, didn't work. I'm pretty sure it's a binary file...