Hi Marina,
Twenty Fourteen is an old theme and it doesn’t use the proper WordPress function for the archive title. They should use <code>the_archive_title()</code> but instead it’s using manual like <code>printf( __( ‘Category Archives: %s’, ‘twentyfourteen’ ), single_cat_title( ”, false ) );</code>. So, this plugin will not work for Twenty Fourteen.
Sorry for that.
Regards,
Sakin