edit: After a lot of searching I found a good english dictionary for my Bebook Mini/ Hanlin v5/ lBook/ Papyre/ EZreader/
To use it you need this lBook firmware, modified by Buggins:
http://files.mail.ru/TJ8JFM
It uses Coolreader 3 to read .txt, .doc, .html, .fb2 or .rtf. To read epubs you just need to rename your file to *.epub.fb2.
After installing the firmware make a folder named "dict" in the root of your SD card and put the .dict.dz and .index files in there.
Now when you open an ebook you can press "3" too look up a word in the dictionary.