I've done this before, but I can't seem to get the subtitle track to default ON on this project. I've turned on every subtitle track switch that I can find and I'm still defaulting with it OFF.
This is in the disk simulation mind you... I have yet to burn an actual test disk... but it should be the same.... shouldn't it?
Click (highlight0 the menu button that starts the movie with subtitles; in the right pane "Button Properties" will display. There, in the Action tab, "Set subtitle track" to OFF, or the Lang of your choice.