I’ve done like you said and it all start work perfect! Thank you!
The problem was in “header-extensions.php”: ’cause I’ve changed “Call us” into russian words, but mysite didn’t show correct russian letters, so I changed encodint tu UTF-8 – then mysite showed me correct russian words, but stoped working sitemap by Yoast.
To change the Call us into russian words you need to create a .po and .mo file and paste your .po and .mo file inside the language directory. But before making any changes first of all you need to create a child theme and create language directory and paste your .po and .mo file