If I switch locale to en_US.UTF-8 then this plugin correctly parses text date and print relative date. But when I mouseover on date I see unusual formating of the date (it uses AM/PM format while russians use 24-h notation).
P.S. All pages but RecentChanges show well-formated date. RecentChanges show date formated using locale. Anyway, plugin does not work without en_US locale.
Fixed. Now it uses C locale for the date put in the title, that is used by relativedate. The mouseover will display the date in your native locale.