type

  TReadThread = class(TThread)
 private
  FText: String;
 protected
  procedure Execute; override;
 public
  property Text: String read FText write FText;
end;


procedure TReadThread.Execute;
var oleVoice: OLEVariant;
begin
    oleVoice := CreateOLEObject('SAPI.SpVoice');
    oleVoice.Speak(ftext);
end;


procedure TForm1.Button1Click(Sender: TObject);
begin
   ReadThread := TreadThread.Create(true);
   ReadThread.FreeOnTerminate := True;
   ReadThread.Text := 'Das ist ein Test';
   ReadThread.Resume;
end;