Get a sample map including the dialog engine here.
If you know how custom text works, you can use v2.0 of my dialog engine. I'll upload it when I feel like, but for now you can get it here.

How to implement SuperIKI's dialog engine to your map

  1. Create a few variables: They don't need an initial value.
  2. Add the trigger 'Show Dialog'.
  3. That's it.

How to create a dialog with this dialog engine

SuperIKI's WarCraft III website