What happend to fonts? Where dissapeared encoding and script selection part? How do I know, what has been set and what has not? This is like major change, why there is no description about that?

Please see this. There are multiple threads in the Bugs forum as well about this.

Simply put... mIRC no longer supports code pages. Everything that can be done in a code page can be done using Unicode without having to ever change a code page to use another language. It's a much better method that has been around for over a decade.

Per Khaled, mIRC will not support code pages in the future either. There are ways to script code page support and there are some scripts being developed that will add code page support through a scripted method, but you are encouraged to switch any channels to UTF8/Unicode so they are visible to everyone. If you absolutely need to have code pages and can't switch to Unicode, then 6.35 works just fine and you'll want to stick to that. The main purpose of updating mIRC to 7.1 is for Unicode support and if you don't need that, then there's no reason to update.

Also, the description of what is changed is in the versions.txt file and on the whatsnew.txt page here.

Oh, Riamus! Haven't seen you for a while

Thanks for answer, now I understand everything.