Is it possible to localize the Mac Welcome Assistant Language to be non English?
Ok, I found the solution.
it looks like there was some problem with preinstalled system.
I just pass through whole assistant in english. And after choosing desired language, the system still was launched still in English. So I ser the desired language in System Preferences, and removed English language.
Then I launched again with Command-R, and reinstalled system.
Now „Welcome assistant” on the begining has language to choose and imidiately changes it to desired language. Perfect.
By the way, sorry for my English ;)