I've install LibreELEC 9.2.6 on to VMWare virtual machine from LibreELEC-Generic.x86_64-9.2.6.ova file. Nothing modified.
After this i've install Locale addon and set UTF8.ru_RU locale. The result can be seen on the screenshots. The third screenshot was made with Arial fonts set in the skin settings.
Perhaps still, not all fonts in the LibreELEC contain symbols to UTF8.ru_RU locale?
Screenshots
In order to see "Рыцари справедливости" as name of your movie, environment should
1. Have "Рыцари справедливости.mp4" file on file system written in utf-8
2. Run filename through windows-1251 to utf-8 converter
3. Display converted output in UTF-8 UI.
That's only one of the ways for breaking it. Step 1 and 2 can be done other way by writing file with wrong name into file system.
I got "На Дерибасовской..." file on generic x86_64 9.2.6 libreelec and it is displayed correctly in ls or GUI. MC displays these characters as question marks, but it does calculate byte length for every ? properly.
Check how you can see those files in ls command output in ssh client that is running in UTF-8. You have to check what you got on your file system before starting to debug MC or Kodi.