Pocketbook has openly developed firmware. It also gives you a windows utility that can convert
XDXF dictionaries to its ".dic" format. You simply copy this file to system/dictionaries folder after attaching to computer via USB and BAM! it is available there when you open your book.
As a result, you have almost all dictionaries free of cost and one of the users SirSteiner here on mobileread has
created one from Wiktionary. I also have linked
Wordnet 2.0 here.