I’ve had some customers in my mobile-home park who have exterior windows that are louvered–they can be adjusted to lie flat or stick out at a right angle to the plane of the window frame.
So far the best way to wash the outside of such windows–long thin pieces of glass set in an aluminum rack–is to stand inside the room and, with the windows open as far as I can turn the crank, wipe both sides with cloth or squeegee. Are there any better ways to do it?