The original Thai language was relatively straightforward:
words were monosyllabic; there were only three tones;
and the range of consonants was limited. However, Thai has “borrowed” words
from other languages extensively. Many religious and medical terms have been borrowed
from Sanskrit and from Pali. Many words were absorbed from Khmer during the
Ayutthaya period, particularly words associated with royalty and aristocracy.
Day−to−day words have arrived with immigrants from China
with their various Chinese dialects. And, more recently, modern words have been adopted from English.
One of the features of the written Thai language is that it tries with loanwords to preserve
much of the original spelling. This means that syllables can end with consonants which
don't "fit" the Thai spoken system, so the pronounciation of the final consonant is changed.
Consider a word such as อาหาร (food). The final ร is pronounced /n/, so it's /aaˑhǎan/.
Final ล is also pronounced /n/, so ผล (fruit) is pronounced /phǒn/.
So, we can start to put together a table of initial and final pronunciations:
(ม, ย, ว, น and ง are (as we've seen previously) pronounced the same in initial and final positions.)