translate arabic to english

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C#

ASP.NET

i am translating arabic text to english ...


but i getting error in this part of method
"result = result.Substring(res1, res2);"

error is :
"

Index and length must refer to a location within the string.Parameter name: length

"

Exception Details: System.ArgumentOutOfRangeException: Index and length must refer to a location within the string.

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string val = "مشرف لوحة أجهزة القياس";
            TranslateText(val, "ar|en");
         }
    }

public string TranslateText(string input, string languagePair)
   {
       string url = String.Format("http://www.google.com/translate_t?hl=en&ie=UTF8&text={0}&langpair={1}", input, languagePair);
       WebClient webClient = new WebClient();
       webClient.Encoding = System.Text.Encoding.UTF8;
       string result = webClient.DownloadString(url);
       int  res1 = result.IndexOf("id=result_box") + 22;
       int res2 = result.IndexOf("id=result_box") + 499;
       int  len = result.Length;
       result = result.Substring(res1, res2);
       result = result.Substring(0, result.IndexOf("</div"));
       return result;
   }