Sure, but jacek was asking for Polish dics:
A good source is
http://enpl.dict.cc/?s=about%3Awordlist. Since they are very generous with their vocabulary database and are asking not to give the dics away, every user should create his dictionary himself. There is one english-german downloadable at the aforementioned site too.
There is a whole thread about dics and conversion here at
https://www.mobileread.com/forums/showthread.php?t=60689
Alberto Pettarin, the creator of Penelope (an universal converter), has his thread here:
https://www.mobileread.com/forums/sho...d.php?t=232883
And the thread here from the very helpful SIRSteiner:
https://www.mobileread.com/forums/sho...d.php?t=190769
For whose who understand German a good source of information is this from yen:
http://www.lesen.net/forum/ebook-rea...bo-außer-firm/
And the the attached file from the last mentioned thread has all the infos in German in it including the tools needed (source yen from the German forum).
EDIT: And for Jacek who is looking for Polish sources, that could be interesting:
http://zabałaganionemiejsce.pl/slownik-sjp-pl/
Conversion should work with penelope but I didn't check it.