Either "Add Bonus Language" does not work (you can select something but it is never applied)
It is displayed when it is not usable and should be hidden
Works fine from what I can see. The dialog comes up and shows you how many choices you have (can be zero) and the options (can be empty until race is selected or if a race without coded bonus languages is selected). Could you provide the scenario you hit please?
No idea. I was diagnosing something for Andrew, but don't recall what. I will cancel and make a new one if I can reproduce