I've found some details about use and locale usage of window directions and some arguments for both choices:
Summing up the claims by Frank Tate:
The direction is more seperated between northern (Scandinavian, UK) versus central and southern countries (Pt, Es, Fr, De, It, ...).
Both solutions have unique advantages in regard to climate and handling:
- Appearence: Inward opening windows are hiding themself behind the frame when they are open.
- Cleaning and Installation: Inward opening windows are same easy to clean from inside and outside. For modern outward opening windows there seem to be solutions as well.
- Flowerpot: Inward opening windows are best decorated from outside, while outwards opening windows are best decorated from inside.
- Shutters: For inward opening windows external shutters can be used. They are providing much better isolation for radiating heat than internal shutters. They also enable ventilation while keeping radiation heat outside.
- Weather: Outwards windows tend to be more resilant to wind and rain, while they have to be secured when open at stormy weather.
- Security: Outwards windows can be more secure.