Which kind of server side code you are using?
In case of php connectors - be sure to use
$sched->set_encoding(“utf-8”); // or any other locale, which need to be used in your case
If you are using java connectors - there is a known issue with non-utf encoding, please contact us directly at support@dhtmlx.com for the update.
If you are using custom server side code - be sure that client side code, database and xml uses the same encoding.