Transliteration is the rendering of the letters of one alphabet by the equivalents of another; transcription is the process of taking the sounds of a language and representing them in a systematic manner.
When we transliterate a Thai word, we replace each character with a corresponding character (or characters) from a different alphabet. Perhaps the only place a learner is likely to encounter transliteration is in Google Translate results. Here are some examples:
From this we can probably guess:
ห → h̄ อ → x ม → m า → ā ◌ี → ī บ → b ก → k
We could then predict:
ออกมา → xxk mā อาหม → xāh̄m กอบ → kxb อีกา → xīkā
And we’d be right.
Conversely, given the transliteration we can reconstruct the original spelling:
māh̄ā → มาหา xxk mā → ออกมา mī māk → มีมาก xxk h̄āk → ออกหาก
The transliteration only tells us about the original spelling of the word – it tells us absolutely nothing about pronunciation – such as whether a character is silent, what the tone of a syllable is, &c.. In short, transliteration is of no relevance to a student of Thai.
In fact, transliteration is a relic of the old days when computers struggled to process complex scripts such as Thai. It was easier for them to work with the transliterated version of the language. Since the widespread adoption of Unicode See What is Unicode? for an explanation of Unicode transliteration is no longer needed, and it’s a complete mystery (to me at least) why Google bothers to show it at all.
For a fuller description of Google Transliteration see Google transliteration for Thai.
Transcription attempts to represent the sounds (not the spelling) of a spoken language. To fully represent the sounds of Thai any transcription system needs de minimis to:
If we consider the official RTGS transcription scheme (การถอดอักษรไทยเป็นอักษรโรมัน) See Wikipedia or สำนักงานราชบัณฑิตยสภา (Office of the Royal Society) for an explanation of RTGS transcription. it fails on every count. For example:
RTGS makes no attempt to indicate tone or stress. In short, it might be a convenient way for marking road signs that foreigners can read to find their way around the country, but it’s utterly useless for learners of Thai.
The transcription used for Thai music videos so that drunken foreigners at karaoke venues can croon along to their favorite Thai songs is similarly useless for Thai learners.
Moving on to good quality transcription, such transcription allows learners unambiguously to know how a word is pronounced. Take as an example the transcription used on this site, if we look at the RTGS examples from above:
Tones are indicated by symbols above the vowel (except for mid tone, for which no symbol is used).
Stress is not indicated since this is generally pretty regular. (In Thai, the last syllable of a word - and the only syllable, for one-syllable words - is always stressed.) Other transcription schemes do indicate this.
So why is transcription important for the beginning Thai learner? For many reasons. Here are a few:
There's more on this in Benefits of transcription.
Good quality transcription can make starting to communicate in Thai much faster than relying solely upon Thai script and avoids the inconsistencies and ambiguities that are inherent in Thai.
And if you ever find yourself mentioning “Thai transliteration”, the chances are you almost certainly mean “transcription”.