Now i have
(set-language-environment "UTF-8")
(prefer-coding-system 'utf-8-unix)
(setq org-export-html-coding-system 'utf-8-unix)
and publishing works perfectly. Funny, that i have every locale set to
"en_US.UTF-8", but LANGUAGE and LC_ALL set to empty. But when i set them to
"en_US.UTF-8", Emacs still opens non-utf8 files as "undecided-unix". In
file-coding-system-alist i found expression ("" undecided) and when i
changed it to utf-8-unix, every file started opening with this encoding.
I've solved my problem, thanks to you all.
I only not sure why opening everything as utf8 wasn't made default in Emacs.
