the dictionaries provided by Bookeen are derived from wikis or GNU/CC sources. (Link: http://188.8.131.52/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:
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.