Although I'm not a native speaker, I would like to comment something you wrote about the use of languages in Luxembourg, i.e.
And now for the reality. Schools teach in all three languages, and the average Luxembourger does speak all three fluently.
In the Luxembourgish school system there are no subjects taught in Luxembourgish, except the Luxembourgish language. Children use only Luxemburgish in the pre-school years and they start with German classes in the primary school, so the teaching of literacy skills takes place in German (as it's the closest language to the language they're supposed to speak at home, which is not always the case due to the large presence of foreigners in Luxembourgish schools...), then French comes later... In high schools some subjects are taught in French, others in German. Although teachers often talk to their students in Luxembourgish, text books are either in German or in French and exams are either in German or in French. This causes a big linguistic issue of course and it's still a major debate in the Luxembourgish society. Luxembourgish dictionaries are more and more available in bookshops and libraries though. Recently, a comprehensive grammar of the Luxembourgish Language has been published in French by the Ministry of Education (Grammaire de la langue luxembourgeoise, Ministère de l'Education Nationale et de la Formation Professionnelle,
As for local newspapers, there are more papers in French now. Even the French version of the "Luxembourger Wort"(La Voix).
Because of this complex and diverse linguistic situation in the country, IMHO I wouldn't state that the average Luxembourger can speak all three languages fluently.
It depends on the location and on many other factors (interests, education, work environment etc.) In more central and northern parts of the countries Luxembourgish is much more used and sometimes even young people can't speak French properly. Along the eastern border German is widespread, but it's a tourist destination, so especially in bars, restaurants and hotels everyone is fluent in at least four languages. However in the South, near the French border, German is never used and even though the average Luxembourger would be able to speak German, I wouldn't generalize saying that they can all speak fluently, especially if they only use Luxembourgish at work and at home. Old people tend to speak German very well since during the German occupation French was not taught at school.
I think some natives prefer reading German newspapers and literature and watching German television. However I know some of them who completed their studies in France and prefer using French in the everyday life...
This is maybe an interesting website:
http://www.eu2005.lu/fr/savoir_lux/soci ... /index.php
I use at least 3 languages every day and I think that it's quite usual over here