Message "Document version exported." generated in Django system locale (LANGUAGE_CODE), not in user defined. If LANGUAGE_CODE is ru-ru, and user locale is English, message will be in russian. screenshot
URLs in message "Document version exported." starts with "http://", but site served via https reverse proxy, leading to NO file download, "Server communication error" popup and mixed content error in Developer console (F12).
Messages not marked as read automatically after actual reading (click on message)