Yeah, yet another "go to our kind user's reverse engineering project...":
Note: I understand that Bookeen does NOT have the commercial power to embed "commercial" dictionaries in its product (you must be "Amazon", "Kobo" or "Sony" to do that, and you must assure the publishers that you are going to encrypt them or make them unaccessible from the end user.) AND I think that the Cybooks are great because they give you some typographic/management features that other eReaders simply do not have. Including the possibility of adding your own dictionaries (now, also Kobo Glo has that).
BUT I am quite annoyed by the fact that Bookeen is not providing an official specification AND that they have not implemented the (rather trivial) menu for letting the user choose which dictionary she prefers.
PLUS, the fact that I wrote them months ago, offering advice (for free!) AND they turned down my offer in a rather swift way, does not help...