Hi,
Yoast outputs the slug based on the site’s set-up. We would expect this to be a non-Yoast issue.
If you visit the URL on the front-end does it show /glavnaja/ as part of the URL?
If so, something on your site is adding /glavnaja/ to the homepage as the slug, as homepages do not usually have slugs.
1. Go to Settings-General and see if /glavnaja/ is listed as part of the WordPress or Site Address fields. If it appears, edit the fields to remove it. If you are unable to edit the fields or those fields do not appear, please contact your host provider to verify.
Note, that before making changes please ensure you have a backup. If you are not sure how to take a backup your host provider can help.
2. If you scroll down on the page in the backend (or look to the sidebar) do you see a section that says slug? This would be some kind of non-Yoast field. See example for what it might look like: https://pasteboard.co/JgpIMqp.png. If you edit that field does /glavnaja/ drop off?
Note, that before making changes please ensure you have a backup. If you are not sure how to take a backup your host provider can help.