Sanjay, I don't think you should follow the Chinese example and extend the CJK range. This was needed because Chinese and Japanese don't use space to separate words. I believe Thai uses spaces, right? If so, you should extend LETTER range to include Thai character rather than CJK.
Another place you would need to change is the LanguageIdentifier. You would either train it, or implement some hack, in order for it to be able to detect Thai language documents that are not of HTML with lang="th" attribute. -kuro
