public class Rootobject
    {
        public string from { get; set; }
        public string to { get; set; }
        public string domain { get; set; }
        public int type { get; set; }
        public int status { get; set; }

        public int error { get; set; }
        public string msg { get; set; }

        public Trans_Result[] trans_result { get; set; }
    }

    public class Trans_Result
    {
        public string src { get; set; }
        public string dst { get; set; }

        public int prefixWrap { get; set; }

        public object[] relation { get; set; }
        public object[][] result { get; set; }
    }

 public static async Task<Rootobject> Baidu_Translate(string content)
        { return await Baidu_Translate("en", "zh", content); }
        public static async Task<Rootobject> Baidu_Translate(string from, string to, string content)
        {
            // 原文
            string q = content;
            // 源语言
            // 改成您的APP ID
            string appId = "";
            Random rd = new Random();
            string salt = rd.Next(100000).ToString();
            // 改成您的密钥
            string secretKey = "";
            string sign = EncryptString(appId + q + salt + secretKey);
            string url = "http://api.fanyi.baidu.com/api/trans/vip/translate?";
            url += "q=" + HttpUtility.UrlEncode(q);
            url += "&from=" + from;
            url += "&to=" + to;
            url += "&appid=" + appId;
            url += "&salt=" + salt;
            url += "&sign=" + sign;
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "GET";
            request.ContentType = "text/html;charset=UTF-8";
            request.UserAgent = null;
            request.Timeout = 6000;
          
            using (WebResponse response = await request.GetResponseAsync())
            {
                using (Stream myResponseStream = response.GetResponseStream())
                {
                    using (StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8")))
                    {
                        string retString = myStreamReader.ReadToEnd();
                        Debug.WriteLine(retString);
                        var result = JsonConvert.DeserializeObject<Rootobject>(retString);
                        return result;
                    }
                }
            }
        }

        // 计算MD5值
        public static string EncryptString(string str)
        {
            MD5 md5 = MD5.Create();
            // 将字符串转换成字节数组
            byte[] byteOld = Encoding.UTF8.GetBytes(str);
            // 调用加密方法
            byte[] byteNew = md5.ComputeHash(byteOld);
            // 将加密结果转换为字符串
            StringBuilder sb = new StringBuilder();
            foreach (byte b in byteNew)
            {
                // 将字节转换成16进制表示的字符串，
                sb.Append(b.ToString("x2"));
            }
            // 返回加密的字符串
            return sb.ToString();
        }

        private async void button1_Click(object sender, EventArgs e)
        {
            var res = await Baidu_Translate(richTextBox1.Text);
            string result = res.trans_result[0].dst;
            richTextBox2.Text = result;
        }