thank you very much for your reply. I figured out that changing fonts is working for mobi files, but pdfs remain the same. The only problem with three characters (č, ć, đ) is present in three pdf files uploaded on the Internet by the same person. All other ebooks in pdf format with Central/East-European character encoding are shown correctly.
I will be patient and hope that the problem be solved by the developers in the following months. I don't dare to downgrade to one of the previous versions now when the installation process went flawlessly
Apart from that, I'm very satisfied with pdf reflow in Duokan. "Smart layout" is great and "cut edges" option can do a proper job where smart layout fails and it comes in handy with pages arranged in two columns (although files like that can considerably slow down turning pages). I was pleasantly surprised when I found the option to turn pages automatically, for all of us lazy people reading in bed
Overall, great job is done by the Duokan team.