How many diphthongs are there in the Russian language?

Answer 1

A phonemic diphthong is a vowel sound which consists of two distinct articulatory parts, but behaves as a single phoneme and forms a single syllable. It is phonemically inseparable, therefore it can be perceived as a single vowel by some native speakers who do not notice its two articulatory parts.

Examples of true phonemic diphthongs in English (sounds, not letters): A in LATE, I in TIME, OI in POINT, O in HOPE, OW in TOWN.

According to this classic definition, Russian does not have any diphthongs.

What is sometimes called "diphthongs" in some Russian courses for foreigners, are not really diphthongs. They are combinations of "a vowel" + "semivowel й". The "semivowel й" is a sound very similar to the one represented by Y in English words like YET, YES, YARD, YOUNG etc.

So, we have combinations like АЙ (май, тайна), ОЙ (слой, пойма), УЙ (дуй, буйвол) and others. They are perceived as two distinct sounds by Russian speakers, and they are morphologically separable (compare: ДУТЬ "to blow" - infinitive - ДУЛ "blew" past - ДУЙ "blow!" imperative, where -Й is a suffix added to the stem).

Then, if the questions actually was "How many combinations of a vowel + й are possible in Russian?" then the answer is:

All the combinations are possible. There are 6 basic vowel sounds in Russian, so all the six combinations with Й can occur: АЙ, ЭЙ, ИЙ, ОЙ, УЙ, ЫЙ. Again, I mean sounds, not letters. In spelling there are more options: ЯЙ, ЕЙ, ЁЙ, ЮЙ are also possible, though they do not represent independent vowels.

The basic pronunciation rule is easy: the vowel quantity itself does not change (irregardless on being followed by Й or not), and Й is pronounce the way it is described above.