Hi Iner,
yes, unfortunately Bookeen does not seem to care about their customers so much...
I reverse engineered the dictionary format used by the Odyssey, and wrote a Python script to convert XML-like or Stardict dictionaries into that format.
Hence, if you have an English-German Stardict dictionary (I saw it around some time ago), you can convert it for using in the Odyssey.
You can find all the required information at the following URLs:
http://www.dei.unipd.it/~pettarin/penelope.html
or
http://code.google.com/p/penelope-dictionary-converter/