New users don't get emails because of language

Problem:
when Russian language is selected in Settings-General-Site Language, then new users never receive emails with a password after they register on the site. Also, the admin doesn’t receive a notification about the new user registration.

The problem is gone when English language is selected as the Site Language.

I installed the Email Log plugin which shows that all the emails are going out ok so it wouldn’t be a server’s fault, I guess.

When Russian language is selected as the Site language, the emails are showing in the Email Log list have only “?” symbols instead of Cyrillic characters in the Subject and the Body of the message.

Could anyone help me figuring out what could be a source of the problem?