Unicode support to insert Arabic words into tally

I am trying to insert data into tally through my C#.net windows application, my code is as below. I am not able to insert arabic data into tally, shows some junk notations instred of arabic text. Is there any other unicode format I need to use? or any code to add?

byte[] tally_req = Encoding.UTF8.GetBytes(Req_builder.ToString());
var http = WebRequest.Create(txtTallyConnection.Text) as HttpWebRequest;
var cache_policy = new RequestCachePolicy(RequestCacheLevel.NoCacheNoStore);
http.CachePolicy = cache_policy;
http.Method = "POST";
http.ContentLength = tally_req.Length;
http.ContentType = "text/xml ; encoding =UTF-8";

using (var write_request_stream = http.GetRequestStream())
write_request_stream.Write(tally_req, 0, tally_req.Length);
using (var tally_reponse = http.GetResponse() as HttpWebResponse)
using (var tally_response_reader = new StreamReader(tally_reponse.GetResponseStream()))
Response = tally_response_reader.ReadToEnd();