The kind of dresses Louise wears for these occasions (as does Elisabeth and other royal children) aren't really a fashion but a classic IMO, that has been around for a long time and will stay. Little girls get dressed up in traditional BCBG dresses, with a ribbon in their hair and varnished shoes ... But I hated them
On the contrary I loved (and still do) everything Astrid Lindgren ever wrote!
I have no idea whether or not Louise is learning Dutch, but I don't think it's important. As long as she learns more than 1 or 2 languages I'm satisfied, I think it's very imoportant for the development of a child, it also broadens your horizon and the way you look at the world. But whether it must really be Dutch for Louise? She'll probably never have an official function to speak of -- and most people in Belgium don't even know her name I guess. Laurent's children don't get the same focus Mathilde's eldest children do (good thing for them!).