Finally I have found the source of my Cyrillic issues. It's the database charset. The SOGo db creation part from smeserver-sogo-0.6-1.el5.nh.noarch.rpm from nethesis repo is creating the database in latin1 charset.
-- SOGo Database Creation
CREATE DATABASE IF NOT EXISTS `sogo`;
CONNECT `sogo`;
CREATE TABLE IF NOT EXISTS `sogo_folder_info` (
`c_folder_id` bigint(20) unsigned NOT NULL auto_increment,
`c_path` varchar(255) NOT NULL,
`c_path1` varchar(255) NOT NULL,
`c_path2` varchar(255) default NULL,
`c_path3` varchar(255) default NULL,
`c_path4` varchar(255) default NULL,
`c_foldername` varchar(255) NOT NULL,
`c_location` varchar(2048) NOT NULL,
`c_quick_location` varchar(2048) default NULL,
`c_acl_location` varchar(2048) default NULL,
`c_folder_type` varchar(255) NOT NULL,
PRIMARY KEY (`c_path`),
UNIQUE KEY `c_folder_id` (`c_folder_id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
CREATE TABLE IF NOT EXISTS `sogo_user_profile` (
`c_uid` varchar(255) NOT NULL,
`c_defaults` text,
`c_settings` text,
PRIMARY KEY (`c_uid`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;