Wrong encoding of subject line in notification email

After migration from 8.4.5 to 11.10.3 the subject line of notification emails is now encoded as ISO-8859-1, all characters replaced with “?” signs now (probably subject is localized).

The body of notification is ok - with national symbols.

Multilanguage is disabled here, default language is Russian.

I've created thread on forum, but it has no answers: https://forum.xwiki.org/t/wrong-encoding-of-subject-line-in-notification-email/6353