I haven't seen this topic here, perhaps due to the fact I was wandering around the world.
I’ve actively studied Luxembourgish in Luxembourg and before going there. I’ve used some of the most common textbooks available and also more linguistics-related books as well. I will leave here some of the references I remember by memory now, aside from the ones from the first video below.
Just take a look on how Luxembourg sounds.
https://www.youtube.com/watch?v=8wN76InEVmQFrom minute 3:58 onwards, you might see some of the references available in the language. I’ve all of them, but they are in another country. I can’t take a look on them. If one day I go back home, I will edit this and add some additional information.
Another resource for those who are curious, other than the Youtube videos:
http://www.vdl.lu/Culture+et+Loisirs/Cours+organis%C3%A9s+par+la+Ville/L%C3%ABtzebuergesch+l%C3%A9iere+mat+MP3+_+Fichiers+audio.htmlOn Luxembourgish resources:Lëtzebuergesch fir all Dag. Book 1 Exercises
Lëtzebuergesch fir all Dag. Book 2 Exercises
Lëtzebuergesch Léiere Mat
http://www.quattropole.org/en/e_learningIf you are into online stuff, you might give it a try. It was working some time ago and the registration is for free. For further information, send them an e-mail.
On grammarIn French
Grammaire de la langue luxembourgeoise. Luxembourg, Ministère de l'Éducation nationale et de la Formation professionnelle 2005 by BRAUN, Josy.
1,2,3 Lëtzebuergesch Grammaire by SCHANEN, François / ZIMMER, Jacqui.
Lëtzebuergesch Grammaire luxembourgeoise. En un volume. Esch-sur-Alzette, éditions Schortgen, 2012 by SCHANEN, François / ZIMMER, Jacqui.
I used resources explained in German and they were pretty accurate. I can't recall their names or authors, unfortunately.
Dictionaries:http://www.lod.lu/index.htmlhttp://www.dico.lu/Luxdico Deutsch: Luxemburgisch ↔ Deutsches Wörterbuch, Luxemburg (Éditions Schortgen) 2008 by WELSCHBILLIG Myriam, SCHANEN François, Jérôme Lulling. (In German).
Klengen Dictionnaire Franséisch-Lëtzebuergesch
http://dict.luxdico.com/deu/http://www.freelang.com/enligne/luxembourgeois.phpAdditional resources for “reading”:
1. Luxembourg and Lëtzebuergesch: Language and Communication at the Crossroads of Europe 1st Edition
This is a book written in English and more designed for linguists. It has some interesting thoughts on historical linguistics or dialectology. It might too dry for those who are not into the field, but I will leave here for others who might be interested in.
2. Lëtzebuergesch Sproocherubriken. Esch-sur-Alzette, éditions Schortgen, 2013 by SCHANEN, François. (in Luxembourgish).
3.
http://orbilu.uni.lu/bitstream/10993/1143/1/Illustrations_Luxembourgish%20-%2017%20-%20revised%20version%20after%202nd%20revision%20-%20mit%20Bilder.pdf4.
http://www.cpll.lu/ortho/intro_ortho.html5. Jérôme Lulling is a linguist from Luxembourg who is (was) working on the preservation of Luxembourgish. Therefore, most of his works were very interesting to me. You might check the external links on here:
https://en.wikipedia.org/wiki/J%C3%A9r%C3%B4me_Lulling6. Gerald Newton is another linguist (professor of Germanic linguistics and Luxembourgish) who has published an amount of articles about Luxembourgish.
Others1.
http://www.insl.lu/Francais/page5/p5frame.htmOn this website you can see what the test to become a citizen of Luxembourg is like. If the law hasn’t changed, one need at least A2 level to take the test, among other non-linguistic requirements.
2.
http://www.luxembourg.public.lu/en/le-grand-duche-se-presente/langues/letzebuergesch/index.htmlWhen I was in Luxembourg, I could converse in both French and German, but the former was much more used than the former one by local people. I used German to talk to my friends as it was (and still is) my “strongest” language, even though they were sometimes speaking to me in French. I feel more comfortable speaking in German.
I was introduced to my friend’s grandmother who spoke to me in Luxembourg, but I was answering her in German and it was okay. I could guess almost everything, perhaps because I already know some features (spoken by Luxembourgian native speakers) that are too obvious to understand by the context. It is an interesting language as well as the Swiss German or the dialects spoken in Germany such as the Bavarian one...
If one day I go back home, I will add here some information on grammar and resources I used.
To the original comment, there are much more Norwegian resources than Lëtzebuergesch. I started with Norwegian, but I'm considering switching to Swedish for personal purposes.