I've bypassed this addon for so long because I'm using Pocketbook and the addon's name screams "I'm for Kindle users only!" You should change its name to Push to e-reader. It was pure coincidence I found out Pocketbook users can use it too.
EDIT. as for localized letters converting to symbols, well, I can't seem to replicate it to send you some sample url to investigate. Hopefully this means problem is gone.
Sadly, there is another problem. I'm premium Wyborcza.pl subscriber, I see fully displayed articles, yet they are sometimes pushed partly - generated file only contains few initial paragraphs.