ISO 11940-2

ISO 11940-2 is an ISO standard for a simplified transcription of the Thai language into Latin characters.

The full standard ISO 11940-2:2007 includes pronunciation rules and conversion tables of Thai consonants and vowels. It is a sequel to ISO 11940, describing a way to transform its transliteration into a broad transcription.

The standard ISO 11940 (to be renamed 11940-1) defines a strict and reversible transliteration of Thai orthography into Latin characters, by means of a host of diacritics. The result bears no resemblance to Thai pronunciation. The additional standard ISO 11940-2 describes a set of rules to transform the transliteration resulting from ISO 11940 based on Thai orthography into a broad transcription based on pronunciation, using only unadorned Latin letters. All information on vowel length and syllable tone is dropped, as well as the distinction between IPA /o/ and /ɔ/.

Although the standard is described as a procedure acting on the Thai orthography, the system is based on the pronunciation. Its rules can therefore be also described in terms of Thai phonology. Prominent features of ISO 11940-2 include:

Transcription is according to pronunciation, not Thai orthography, especially notable in final consonants. Vowels are transcribed in sequence as pronounced, not as written in Thai script. Implied vowels, which are not written in Thai script, are inserted as pronounced. Written silent letters are omitted.

The result of applying the rules described in the standard is almost identical to the transcription defined by the Royal Thai General System of Transcription. One exception is preceding a syllable initial vowel by ⟨'⟩, representing the Thai null consonant อ, obviating the need to insert a dash in some words to preserve syllable boundaries. The other exception is the retention of the aspiration characteristic of the alveolo-palatal affricate. So while Thai ฉ, ช, and ฌ, are represented by ⟨ch⟩ as in RTGS, the Thai letter จ is written as ⟨c⟩.

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