What language to speak in Luxembourg?

I am one of those people who thinks that the most significant step towards integration in any country and culture is learning the local lingo. This is true for Luxembourg as well, but still: My advise to any expatriate coming here is simple: LEARN FRENCH! It might not be the local language, but pretty much everybody here speaks it and every important official document is translated into French. It is possible to survive in Luxembourg speaking only English, but you will never get the most out of the place. Learn French and you're 90% integrated. Learn Luxembourgish and you're a star.