Export to CSV did not show correctly for unicode character "???????"

Hi,
Please, can anyone give me idea which UTF I have to used for unicode character to show correctly in csv format when I export out.
Here is my code. I tried with too many UTF like UTF7, UTF8, UTF32, UTF-16, ISO-8859-4 ... and so on.
But still can't show correctly for this unicode character "????????????????????????????" .
Thanks in advanced.
 HttpContext.Current.Response.Charset = "ISO-8859-4";  HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.GetEncoding("ISO-8859-4");  HttpContext.Current.Response.Clear();  HttpContext.Current.Response.Buffer = true;  HttpContext.Current.Response.AddHeader("content-disposition", "attachment;filename=DataTable.csv");  HttpContext.Current.Response.ContentType = "application/text";