Translate text in other languages in asp.net C# web application

asp.netc#-4.0google apiweb services

I want to translate text in Indian languages. I have gone through many articles but can not understand clearly how to do so. I have also seen some articles on google translator but none of them provide guide to use it in code.
Please guide me how can I do so. Do I need to add fonts for all languages in my application?

I have pasted the following code and now getting error. Can't understand what is that error.
The error is "Index and length must refer to a location within the string.
Parameter name: length".

Below is my code.

 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);
    result = result.Substring(result.IndexOf("id=result_box") + 22, result.IndexOf("id=result_box") + 500);
    result = result.Substring(0, result.IndexOf("</div"));
    return result;
}
protected void btnTranslate_Click(object sender, EventArgs e)
{
    string convertTo="en|"+ddlLanguages.SelectedValue;
    txtTarget.Text = TranslateText(txtLanguage.Text, convertTo);
}

ID of both the textboxes are "txtLanguage" for source language and "txtTarget" for target language.

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