I was taught to do it that way in public school here in Canada in the 90s; it is the textbook proper way to spell words like coördination. I was also taught that no one actually spells it that way and that co-ordination and coordination are both fine and far more common.
Apropos of nothing, except that it will allow me to vent a bit, it also changes the rule for the pronunciation of the last consonant of French words.
Normally the lack of a trailing "e" would mean the last consonant is not-sounded but the diaeresis changes it: maïs/"my-isz", Noël/"noh-ell", etc.
And yes Moët (the champagne) is pronounced "moh-ett" in France and by French speakers.
It's incredibly annoying having someone subtly but in a slightly superior manner "correct" your pronunciation by repeating the mispronunciation right after you've pronounced it correctly - "sure, I'll order some some MOHAY". Outside I'm smiling and nodding pretending not to notice, inside I'm screaming "IT'S MOH-fcking-ETT MTHERF*KER - MOH-ETT."
This was a very well explained distinction, with the exception of you using "Noël" as one of the examples, since "Noel" would still have a sounded "L". It would be weird to a French speaker but would most likely end up being pronounced somewhat like the English "null".
> And yes Moët (the champagne) is pronounced "moh-ett" in France and by French speakers.
My favorite Moët mispronunciation is one that it took me several months to understand: Russians pronounce it as if it was spelled in Cyrillic, so they say "mah- yacht".
There is a famous MORGENSHTERN song which I only understood was about champagne when I saw the music video for the first time.
Do you have reason to believe it's true, or are you commenting to say that it would have been a well-explained distinction if it were true?
I tried to verify it, and found nothing but evidence that implicitly or explicitly contradicted it.
(The best I could find in favor were the English wikipedia page on the house of Perrier-Jouët, which lists a pronunciation with /t/ -- the French page lists no pronunciation at all -- and the 19th-century book Comment on prononce le français, which confirms that maïs is pronounced with a final /s/, but lists it without comment alongside several other words that feature the same irregular pronunciation of "-s", none of which include a diaeresis. I'm compelled to infer that the realization of /s/ in maïs has nothing to do with the diaeresis.
https://archive.org/details/commentonprononc00martuoft/page/... , page 302)
It only affects the diphthong AFAIK, so I agree with you that it's not the reason for why the "s" is pronounced out loud.
The final "s" is usually silent in French and I'm not aware of any rule for what defines the exceptions.
The outcome for the final "-s" is somewhat influenced by the origin of the word, as you would pronounce "bis" differently depending on whether you mean "beige" or half-whole-wheat bread, vs. if you mean "repeated" (from latin).
There are a bunch of such weird exceptions, like "vis" (screw, or past tense of "to see") or "bus" (bus, or drank) which both can be pronounced either depending on their meaning, or "os" which is different depending on plural vs. singular.
For the ending "-s" there is also some regional variation. Where I was born, you would normally pronounce the final "s" in words like "plus" or "moins", and I was very surprised as a teenager to meet people from other French regions who made fun of it.
I don't think there is a rule. The 19th-century book said this:
>> L's s'est maintenu ou définitivement rétabli depuis plus ou moins longtemps dans maïs, jadis, fi(l)s et lis (y compris fleur de lis le plus souvent, malgré l'Académie); dans metis, cassis, vis (substantif) et tournevis. La prononciation de ces mots sans s est tout à fait surannée; on ne peut plus la conserver que pour les nécessités de la rime, et encore!
The reference to /s/ being maintained or reestablished, and the pronunciation without /s/ being out of date, suggests to me that the rule was that final /s/ was lost (in Parisian French, I guess...), and that there was a specific effort to put it back into some words. But that's speculation on my part.
It seems clear that bus "bus" and maïs "maize" have a final /s/ because they are foreign words. It's less clear to me why they're given those spellings as opposed to something more like busse.
https://fr.wiktionary.org/wiki/Mo%C3%ABt
> Moët \mɔ.ɛ\
> Nom de famille.
For the champagne, we see this heading the French wikipedia page:
> Moët & Chandon (prononciation /moɛt‿e ʃɑ̃ˈdɔ̃/) est une maison de Champagne fondée en 1743
But that doesn't imply that there is a /t/ pronounced in "Moët" when not followed by a vowel; that's just normal French liaison. The explicit liaison marker in the phonetic spelling strongly implies that there isn't a /t/ in citation pronunciation.
This is all wiki information though - do you have a better source?