> Consider the word “de rien”. It is so simple. Three syllables.
Not that it changes your point, but "de rien" is two syllables!
Not that it changes your point, but "de rien" is two syllables!
Japanese, for example, has "desu" (a form of "to be" so it's really common) which is nominally "two" syllables, but English speakers simply hear "dess" which they perceive as one syllable.
The issue is that Japanese relies more on time length to delineate syllables while English relies on vowel presence.
English speakers would be tempted to think it as a three syllable phrase because ʁjɛ̃ isn't a possible syllable in English, but in French "de rien" should be two syllables.
This is similar to, e.g., English speakers incorrectly pronouncing the Spanish word "luego" with three syllables.
I'm sure that's true, but I don't think it gives rise to any real doubt as to the syllable count. For example, you could stretch out the English word "near" into two syllables in very slow and deliberate speech, but it's definitely a monosyllabic word in most (possibly all?) varieties of English.
For "rien" in particular, I'd say speakers can do that diaeresis as a sort of emphasis. For instance "Tu n'as rien fait! Rien! ("you did nothing! Nothing!"). The first "rien" can be said as a single-syllable world, while the second one can be pronounced as a two-syllables.
It also may be pronounced slightly differently in various places in France (regional accents).
seu-teu-ra-i-keu
(Well, to be fair, it's more like "an awful lot of sounds that have no business being in the same syllable merged together", and less "five distinct syllables", but still that's how Koreans end up writing the sound in Korean.)