This is on Dev Branch and the issue has been here for a while. When selecting "Effects" in a Trigger (or Waypoint), and you select "Text," it doesn't give you the option to type in text to display when the Trigger (or WP) has been activated.
This happens in both the 2D and 3D editor. If you have a mission that was saved prior to the last stable, then the Effect will still function, but once you resave the mission in current versions, it loses the properties to display it. {F27890}