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The Royal Thai General System of Transcription (RTGS) is the official system for rendering Thai language words in the Latin alphabet. It is used in road signs and government publications, and is the closest thing to a standard of transcription for Thai, though its use by even the government is inconsistent.
combinations with "h" as "ph", "th", "kh" are used for aspirated p, t, k, similar to IPA [pʰ, tʰ, kʰ], to distinguish them from the separate unaspirated "p", "t", "k"
uses "ng" for engma as in English, IPA [ŋ]
uses "ch" for IPA [tɕʰ] and [tɕ]
uses "y" for IPA [j]
note that transcription of consonants in final position is according to pronunciation, not spelling
Criticism
The Royal Thai General System has been criticized as inadequate for learners of Thai, particularly because of the following shortcomings:
notation "ch" does not differentiate between IPA/tɕ/ and IPA /tɕʰ/ (see table below)
notation "o" does not differentiate between IPA /ɔ/ and IPA /o/ (see table below)
Letter 1
Letter 2
RTGS
Thai
IPA
Description
English
Thai
IPA
Description
English
ch
จ
tɕ
alveo-palatal
affricate
as "ty" in "let you"
ฉ, ช, ฌ
tɕʰ
aspirated alveo-
palatal affricate
as "ch" in "check"
o
โ–ะ, –
o
close-mid back
short rounded
like "oa" in "boat"
เ–าะ
ɔ
open-mid back
short rounded
like "aw" in "raw", but shorter
โ–
oː
close-mid back
long rounded
like "oa" in "moan"
–อ
ɔː
open-mid back
long rounded
like "aw" in "raw"
Transcription table
For consonants, the transcription is different depending on the location in the syllable. In the section on vowels a dash ("–") indicates the relative position of the initial consonant belonging to the vowel.