Sending Persian word to mikrotik-C#

RouterOS Scripting
1

hi
I tried to set comment to IP address in dhcp/leases by c#,but when i sent some Persian word it shows as ??? .here is my code,please help.

            string myString = "ریاحیان";
            byte[] bytes = Encoding.Default.GetBytes(myString);
            myString = Encoding.UTF8.GetString(bytes);
          
          
            mikrotik.Send("/ip/dhcp-server/lease/comment");
            mikrotik.Send("=.id=" + "*107E6");
            mikrotik.Send("=comment=" + myString, true);
            mikrotik.Read();