Default search engine depends of country code in Local State file. Solution:
Opera's menu > About Opera, and copy path to the profile, close the Opera. Open a terminal window, and type cd, press space, and paste the path, press enter, type gedit Local\ State, and press enter, find the lines:
"country": "XX", "country_from_server": "XX",and check if XX=RU, and if not, replace it with "RU", save the changes, close the file, and launch the Opera, then repeat the steps, mentioned above
Thanks to L33t4opera: http://blogs.opera.com/desktop/2015/03/bookmarks-syncing-opera-28/#comment-1905511416