Q:

On Lao triphthongs / tones / orthography

Information on the Lao language is a bit patchy, especially when you start getting a little deeper and find gaps, inconsistencies, and contradictions in and between sources on the Internet.
Lao vowel sounds are spelled using one or more vowel characters and a couple of characters which are also used for consonants or semivowels. There is a distinction between long vowels and short vowels which plays an important part in determining the tone of a syllable.
Various articles give lists of vowels and diphthongs and tables relating them to their spellings, their length, and their tone. But some words cannot be analysed using just the information in these sources:

ເຂົ້າໜຽວ "sticky rice" /khao niao/

The second syllable appears to contain a triphthong, "ຽວ". Each of the letters "ຽ" and "ວ" can be used either alone or in combination with other letters, but none of the sources I can find mention them in combination with each other.
As vowels "ຽ" usually represents    /iːə/ and "ວ" usually represents /uːə/.
As a consonant or semivowel "ວ" usually represents [ʋ] or [w] (depending on dialect).

So what is this "iao" sound in the "niao" of the second syllable? Or should I regard it as two syllables?
How can I reconcile this with Wikipedia's assertion that "Diphthongs are all centering diphthongs with falling sonority"?
Where does the "ao" come from in this combination, is it the same sound that is usually spelled "ເ-ົາ" as seen in the first syllable of the word?

A:

"ໜຽວ" is 1 syllable, "ຽ" /iːə/ is a typical Lao diphthong with falling sonority, and "ວ" is a consonant /w/, so this is a CVC-type syllable, /n/-/iːə/-/w/, /niːəw/. Note, that /w/ is allowed as the coda in Lao syllables (See A Grammar of Lao, p. 35, section "3.3 Final consonants." Lower on that page there is a list of Lao vowel phonemes and there are no triphthongs there).
Also, /iːə/ is written as "ຽ" only before final consonants, in open syllables /iːə/ is written as ເ◌ຍ, that is another proof that ວ" is onsonant /w/ here. (See this paper, pp. 10-11)
In the first word, the "ເ-ົາ" stands for a combination of a vowel + consonant, /aw/, so the two words have just one thing in common, they both end in /w/. However this /w/ is realised phonetically and acoustically in the coda, it is still the same phoneme as /w/ as the initial consonant. Transliterating this /aw/ as "ao" is just a convention.

