Vietnamese is spoken primarily in Vietnam.
Vietnamese (of Hanoi) has six tones
distinguished by level, contour and laryngeal features.
/p/ only occurs finally and can be analyzed as an
allophone of implosive /b/, but no general rule that
voiced initials pair with voiceless final stops can be
formulated. Vowels in open syllables are followed by a
consonantal offglide (/j/ after /i, e/ etc.). /j, w/ can
follow most vowels, when no other consonant may appear,
but some final consonants can follow the diphthongs with a
low final element.

Canh, N-p. 1974. A contribution to the phonological
interpretation of the diphthongs in modern Vietnamese.
Acta Universitatis Carolinae-Philologica. Phonetica
Pregensia IV: 133-142.

Thompson, L.C. 1965. A Vietnamese Grammar. University of
Washington Press, Seattle.