Christian said:
It is correct that official circles recourse to mostly French, despite technically being allowed to use Luxembourgish. It is ironic that they feel more comfortable writing French, a difficult language with a complex grammar, then Luxembourgish, a simple dialect with an easy grammar.
However IMO there are other more important reasons for the preference of French, such as prestige and most of all the lack of vocabulary in Luxembourgish. It is difficult (one could say impossible) to express complex or abstract ideas in Luxembourgish without having to use French or German words, so when it comes to official announcements and such they prefer to simply go with one or the other, and often the announcements are published in both.
The prestige is a key factor, but the simple dialect with easy grammar becomes difficult to use because there are certain limiting factors when using that easy grammar. In official communications and through official media, complexity of language is required. Think of bank account details, legal speech or acts of government. These
need more complex grammar in order to avoid imprecisions and questions of interpretation. These are harder to do in Luxembourgish with its simple grammar than French and German with their more complex, codified grammar (in which case, Luxembourgish needs to build up its prestige vocabulary and how it deals with situations in which French would use complex grammatical tenses not available to the Lëtzebuergesch speaker).
@Libertine: I have a point of inquiry though:
To my knowlegde Luxembourgish is one of the very few languages to have a masculin/feminin for the number 2: zwee (m) and zwou (f). The only others I know are Russian (dva and dvye IINM) and Portuguese (dois and duas). Do you know any others? Is there a name for this linguistic phenomenon?
Dialectally, you will find Zwo and Zwei in German, but this is little more than regional archaism now. Hebrew definitely divides numerals based on gender at least historically, and I suspect Arabic may do.
As Portuguese, Russian and Luxembourgish are from three very distinct branches of the Indo-European family it is probably an archaism that has been retained only by a few languages. The Portuguese case could also be the result of influence from Arabic - the days of the week in Portugal follow the Arabic pattern, for example. It could also be a remnant of the grammatical dual which has all but died off in most Indo-European languages (singular vs. dual vs. plural). I'm not sure what the origin of the feature is to be totally honest.
Also, I've noticed that you keep writing péloton, and have been wondering whether this is correct - my French autocorrect suggests it is written without an accent. It might be one of those words like Lubéron/Luberon which you find in the two spellings.
I've seen it both with and without. I first saw it with the accent and type that out of habit, but I think I see it without more often.
Except in Spanish, where I always see pelotón.