Hi,
the dictionaries provided by Bookeen are derived from wikis or GNU/CC sources. (Link:
http://176.31.234.27/dic ) That is, they do not offer the same accuracy of commercial dictionaries, like those provided out-of-box by e.g. Sony devices.
However, you can make your own dictionary for the Odyssey with Penelope, a Python tool I developed:
http://code.google.com/p/penelope-dictionary-converter/
http://www.albertopettarin.it/penelope.html
This means that, if you already have a "good" dictionary, in Stardict or XML-like format, you can convert it and use it on the Odyssey.