And I wondered about it, but I assumed you knew better, so I copied you.
So now we have the Luxemboughish / American guy copying the German guy writing German in English. Sorta.
Got it! Clear as mud. 
We also got the Spanish-German guy who started the kerfuffle about the Wilhelms. 
(and corrected this German guy’s misspelling)
Can Luxembourgish speakers understand German speakers, and vice versa?
And, yes, this has been a fun and educational thread. You’ve made me want to visit Luxembourg.
In Germanic-Language countries, a prince (German Fürst) ranks below a duke (German Herzog).
In Italian, Spanish, and Portuguese, a Principe ranked above a duke.
During the ancien régime, France made it even more confusing. Native French princes ranked below dukes, but visiting foreign princes were given ceremonial precedence above native dukes.
At some point (I think during the 19th Century), the diplomats just said “F*** it, every Head of State is equal to every other Head of State.”
One more thing: Liechtenstein’s and Monaco’s princes are styled His/Her Serene Highness. Luxembourg’s monarch is a Royal Highness, a couple of grades higher.
The Luxembourgers got the promotion partly because they are heirs to the Napoleonic kingdom of Etruria, and partly because they are a branch of the Bourbons, and cousins to the French and Spanish royal families.
That must have made it a nightmare to set up seating charts for state dinners.
Nitpick: it’s not a Grand Duchy, but rather the Duchy of Grand Fenwick. I’ve sometimes made the same mistake, so I understand the confusion.
Not easily.
There are some individual words in common (“bad” = schlecht in both Lux. and German; ditto “boring” = langweilig), and some words are fairly close (“maybe” = vielleicht in German, vläicht in Lux, which sounds like the German word if you apostrophize the first diphthong; “together” = zusammen in German, zesummen in Lux). Other words are clearly related when you know (“but” = aber in German, pronounced like ‘obba,’ vs awer pronounced ‘ovva’ in Lux; “to drive” = fahren in German vs fueren in Lux; “child/children” = Kind/Kinder in German vs Kand/Kanner in Lux), but the sound is sufficiently different that it slides past the ear.
Plus the verb conjugation in Lux. is all wonky compared to German. The infinitive form of most verbs ends in “-en,” like fahren above, or spielen, “to play.” Except for irregulars, you normally use that form with the subject “we” or “they” — wir spielen, sie spielen. But in first person, you conjugate: ich spiele. By contrast, in Lux., you use that infinitive form in first person: ech spillen. The infinitive “to be” in German is sein (“zyne”), which becomes sind for we/they, but in first person, you say ich bin (I am). In Lux, you say ech sinn.
Plus there’s a fair amount of vocabulary taken from French and Dutch. For example, if you want to refer to a work rotation in German, you might say die Rotation (“dee roh TA see OHN”). But in Lux, you use a French-derived word — Roulement (capitalized because it’s a noun).
If you put written German and written Luxembourgish next to each other, you can pretty easily map one to the other (er wohnt in einem Haus → hie wunnt an engem Haus → he lives in a house). But when being spoken, all these little differences add up. The German speaker hearing Luxembourgish will notice words every now and then they recognize, but the overall effect is that it sounds like a drunken soup of almost but not quite German.
The Luxembourger listening to a German speaker, by contrast, will have no trouble at all, because the Luxembourger speaks German. And French. And English. And probably some Portuguese. And… 
Don’t forget the befuddled Canadian!
What do Luxembourgers thing about Belgian Luxembourg? Is there any confusion over sharing the name?
Germanic-Language countries, a prince (German Fürst) ranks below a duke
And just to confuse, in the Holy Roman Empire, there were Kurfürsten, usually known in English as “Electors”, who formed the electoral college for choosing the Emperor. And they had various reforms and reorganisations before the republic
As spoofed on Goodness Gracious Me with Guru Maharishi Yogi, “His Most Serene Calmness.”
Thank you! I really appreciate the detail. It’s fascinating. Languages, to me, always are.
@Saint_Cad Following up with a news article on the teacher situation here, in case you want to do a little more homework.
So Parisians think Provençals smell really good?
I’ve actually been to Luxembourg and while I don’t keep up with daily news I am aware of the monarchy and it’s succession.