问谷歌翻译V2无法完成C#的大文本翻译

EN

String apiUrl = "https://www.googleapis.com/language/translate/v2?key={0}&source={1}&target={2}&q={3}";
            String url = String.Format(apiUrl, Constants.apiKey, sourceLanguage, targetLanguage, text);
            Stream outputStream = null;

        byte[] bytes = Encoding.ASCII.GetBytes(url);

        // create the http web request
        HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
        webRequest.KeepAlive = true;
        webRequest.Method = "POST";
        // Overrride the GET method as documented on Google's docu.
        webRequest.Headers.Add("X-HTTP-Method-Override: GET");
        webRequest.ContentType = "application/x-www-form-urlencoded";

        // send POST
        try
        {
            webRequest.ContentLength = bytes.Length;
            outputStream = webRequest.GetRequestStream();
            outputStream.Write(bytes, 0, bytes.Length);
            outputStream.Close();
        }
        catch (HttpException e)
        {
            /*...*/
        }

        try
        {
            // get the response
            HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse();
            if (webResponse.StatusCode == HttpStatusCode.OK && webRequest != null)
            {
                // read response stream 
                using (StreamReader sr = new StreamReader(webResponse.GetResponseStream(), Encoding.UTF8))
                {
                    string lista = sr.ReadToEnd();

                    DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(TranslationRootObject));
                    MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(lista));
                    TranslationRootObject tRootObject = (TranslationRootObject)serializer.ReadObject(stream);
                    string previousTranslation = string.Empty;

                    //deserialize
                    for (int i = 0; i < tRootObject.Data.Detections.Count; i++)
                    {
                        string translatedText = tRootObject.Data.Detections[i].TranslatedText.ToString();
                        if (i == 0)
                        {
                            text = translatedText;
                        }
                        else
                        {
                            if (!text.Contains(translatedText))
                            {
                                text = text + " " + translatedText;
                            }
                        }
                    }
                    return text;
                }
            }
        }
        catch (HttpException e)
        {
            /*...*/
        }

        return text;
    }