In \includes\functions\functions_general.php i removed the STRTOLOWER() part by changing

PHP Code:
function zen_parse_search_string($search_str = '', &$objects) {
$search_str = trim(strtolower($search_str)); 
to

PHP Code:
 function zen_parse_search_string($search_str = '', &$objects) {
$search_str = trim($search_str); 
and it seems to be working fine with both Cyrillic and English chars but i guess it may lead to some other kind of problems with the search modlue.Any suggestions of a better solution to this issue are welcome.