/// <summary>
        /// Download lang model
        /// </summary>
        /// <param name="sourceLangCode"></param>
        private async void DownloadModel(String sourceLangCode)
        {
            MLLocalTranslatorModel  model            = new MLLocalTranslatorModel.Factory(sourceLangCode).Create();
            MLModelDownloadStrategy downloadStrategy = new MLModelDownloadStrategy.Factory()
                                                       .NeedWifi() //  It is recommended that you download the package in a Wi-Fi environment.
                                                       .Create();
            Task downloadModelTask = manager.DownloadModelAsync(model, downloadStrategy);

            try
            {
                await downloadModelTask;
                if (downloadModelTask.IsCompleted)
                {
                    // Delete success.
                    this.DisplaySuccess("Download success.", true);
                }
                else
                {
                    // Delete failure.
                    Log.Debug(Tag, " Download failure.");
                }
            }
            catch (Exception e)
            {
                // Operation failure.
                DisplayFailure(e);
            }
        }
        /// <summary>
        /// Delete lang model
        /// </summary>
        /// <param name="langCode"></param>
        private async void DeleteModel(string langCode)
        {
            MLLocalTranslatorModel model = new MLLocalTranslatorModel.Factory(langCode).Create();

            Task deleteModelTask = manager.DeleteModelAsync(model);

            try
            {
                await deleteModelTask;
                if (deleteModelTask.IsCompleted)
                {
                    // Delete success.
                    this.DisplaySuccess("Delete success.", true);
                }
                else
                {
                    // Delete failure.
                    Log.Debug(Tag, " Delete failure.");
                }
            }
            catch (Exception e)
            {
                // Operation failure.
                DisplayFailure(e);
            }
        }