Pronunciation of the letter sequence vowel + ill + a in the name "Guillard"

Question

According to various online sources (1, 2), in the letter sequence vowel + ill the ll should be pronounced as the English "y", or [j] in the IPA. This rule seems to apply in general, e.g. in the word "cuillère": [kɥi'jɛʁ].

According to the German wikipedia however, the Guillain–Barré syndrome, named after the Rouen-born neurologist Georges Guillain, is to be pronounced [ɡilɛ̃ baˈʁeː zʏnˈdʀoːm] with ll being pronounced as [l] instead of [j] (note that syndrome is supposed to be pronounced in German). The German Wikipedia explicitly notes that the pronunciation [ɡiˈjɛ̃ baˈʁeː zʏnˈdʀoːm] with ll being pronounced as [j] is frequent, but wrong ("häufig, aber fälschlich").

The English Wikipedia on the other hand suggests the pronunciation ​[ɡijɛ̃] for the name Guillain in the respective article on Georges Guillain with ll being pronounced as [j]. The pronunciation is unsourced in both the German and the English articles.

In this French youtube video (mark 00:03) on the syndrome the name seems to be pronounced as [ɡilɛ̃] concurrent with the German article.

Due to my poor capabilities in the French language, I couldn't think of any other words with the combination vowel + ill + a apart from the name Guillaume, in which ll is obviously pronounced [j].

I would highly appreciate if someone could:

1. Confirm that the pronunciation [ɡilɛ̃] is correct/common.
2. Clarify whether an actual rule for this pronunciation exists, e.g. that in the combination vowel + ill + ai + consonant (as in Guillain), [l] is correct, whereas in other combinations with vowel + ill + a as in Guillaume [j] is correct. Or, perhaps, whether the question comes down to idiosyncratic pronunciation of proper nouns, which is bound to history/tradition rather than rule books.

There seem to be a few French place names containing the sequence vowel + ill + a (Fuilla, Quillan), but I failed to figure out their pronunciation (I would be interested to find out though).

Answer 1

1. [ɡilɛ̃] is definitely the expected¹ pronunciation of Guillain. This last name is certainly a variant of the (first) name Ghislain (Saint- Ghislain was at some point written Saint-Guillain). That can also be written Guislain also pronounced [ɡilɛ̃]. Unfortunately, the alternate (and incorrect) pronunciation [ʒislɛ̃] is spreading and by far the most common in France and Canada now. In any case, there is never a [j] in these pronunciations.
2. ..[vowel]+illa is as far as I know always pronounced with a [j] in French words, I can't find a single exception. The proper names Fuilla and Quillan are also pronounced with a [j] as their Occitan/Catalan form show (Fullà/Quilhan).

Guillain is not really an exception because its u is not technically a vowel but only there to keep the hard [g] sound before an i. Otherwise g would be pronounced [ʒ].

Same goes with Guillard. There is no definitive rule for pronouncing the double l in "illa"/"illain" but a [j] is largely dominating. I would then expect either [gijaʁ] or [gɥijaʁ]. There are only few cases of [l] like villa, villages, chinchilla, capillaire, villain (modern spelling: vilain) and ... arguably Guillain.

¹_{I write "expected" pronunciation because as Quentin Ruyant also commented, there is often no rule for proper names. Georges Guillain's family might have decided that their name is to be pronounced some other way but IMHO [gijɛ̃] is more than improbable although the one often documented in English dictionaries.}

Answer 2

What Dr. Guillain called himself would seem to be most important. See Pronunciation of Dr Georges Guillain's name JAMA. 1977;237(23):2470

Answer 3

I am a french speaking Canadian. I have never heard anybody saying ʒislɛ̃ . There is a some question between gijɛ̃ and gilɛ̃. I've learned in university and in neurology formation the use of gijɛ̃ . Since Dr Georges Guillain was french and my french cousin "dda" up here confirms in France everybody uses gijɛ̃ , that ends the debate for me , thank you !!