The movie is mostly produced under french funds, like most of his recent movies. (the exceptions being the obvious US remake of Funny Games and The White Ribbon, which was supposed to be a movie about the birth of totalitarism and needed the german setup)
Hanneke himself lives in France, I think (not really sure about that) and he can speak french very well.
~ To reduce the numbers of unhappy people, always beat up the same individuals ~

I don't know the answer but perhaps he had Huppert in mind for Erika when he was adapting the screenplay.
I'm a fountain of blood
In the shape of a girl