using System;
using Windows;

namespace SampleSynthesis {
  class Program {
    static async System.Threading.Tasks.Task Main(string[] args) {

      var synth = new Windows.Media.SpeechSynthesis.SpeechSynthesizer();
      Windows.Media.SpeechSynthesis.SpeechSynthesisStream stream =
          await synth.SynthesizeTextToStreamAsync("I want to listen to this text");

      using (var reader = new Windows.Storage.Streams.DataReader(stream)) {
          await reader.LoadAsync((uint)stream.Size);
          Windows.Storage.Streams.IBuffer buffer = reader.ReadBuffer((uint)stream.Size);
          Windows.Storage.StorageFile file = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("audio.wav");
          await Windows.Storage.FileIO.WriteBufferAsync(file, buffer);
    }
  }
}

"C:Program Files (x86)Microsoft Visual Studio2019BuildToolsMSBuildCurrentBinRoslyncsc.exe" /r:"C:Program Files (x86)Reference AssembliesMicrosoftFramework.NETFrameworkv4.5.2System.Speech.dll","C:Program Files (x86)Reference AssembliesMicrosoftFramework.NETCorev4.5System.Runtime.WindowsRuntime.dll","C:WindowsMicrosoft.NETFramework64v4.0.30319System.runtime.dll","C:Program Files (x86)Windows Kits10UnionMetadata10.0.17763.0Windows.winmd","C:WindowsMicrosoft.NETFramework64v4.0.30319System.Threading.Tasks.dll" tts.cs

Unhandled Exception: System.InvalidOperationException: The process has no package identity. (Exception from HRESULT: 0x80073D54)
   at Windows.Storage.ApplicationData.get_Current()
   at SampleSynthesis.Program.<Main>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at SampleSynthesis.Program.<Main>(String[] args)