It is as simple as in the Likebook (just copy the dictionary into the right folder) but you have to use different dictionary formats. Since the Likebook is using Stardict format, you have access to a lot of available dictionaries, some of them of doubtable origin. Pocketbook is using another format but gave us a (simple) converter to create some. If you would rather use Stardict dictionaries, install KoReader on your Pocketbook which does support Stardict format though doesn't support hard DRM.
PS: KoReader is also recommended for learning other languages since it has included a vocabulary trainer.
PPS: If you are looking for some premade Pocketbook dictionaries, this thread might be of help:
https://www.mobileread.com/forums/sh...d.php?t=325203