Words R Us - Indonesian Phrasebook

It is usually said that there are six vowels in Indonesian. These six vowels are shown in the table above. However, other analyses set up a system with other vowels, particularly the open-mid vowels /ɛ/ and /ɔ/.

Diphthongs

Some analists claim that Indonesian has three native diphthong phonemes only in open syllables, they are:

/ai̯/: kedai ('shop'), pandai ('clever')
/au̯/: kerbau ('buffalo')
/oi̯/ (or /ʊi̯/ in Indonesian): dodoi, amboi
Others assume that these "diphthongs" are actually a monophthong followed by an approximant, so ⟨ai⟩ represents /aj/, ⟨au⟩ represents /aw/, and ⟨oi⟩ represents /oj/. On this basis, there are no phonological diphthongs in Indonesian.
[43]

Diphthongs are differentiated from two vowels in two syllables, such as:

/a.ʔi/: e.g. rayakan ('celebrate') [ra.ʔi], air ('water') [a.ʔer] (or [a.ʔɪr] in Indonesia and [a.ʔir] elsewhere) /a.ʔu/: bau ('smell') [ba.ʔu], laut ('sea') [la.ʔot] (or [la.ʔʊt] in Indonesia and [la.ʔut] elsewhere)

Sources:
Clynes, A (1997). "On the Proto-Austronesian 'diphthongs'". Oceanic Linguistics. 36: 347–362. doi:10.2307/3622989.
Soderberg, C. D.; Olson, K. S. (2008). "Indonesian". Journal of the International Phonetic Association. 38: 209–213. doi:10.1017/s0025100308003320.
Wikipedia
Yunus Maris, M. (1980). The Indonesian Sound System. Kuala Lumpur: Penerbit Fajar Bakti Sdn. Bhd, page 2.

Vowels

Diphthongs

English Russian Dictionary