Hi again,
if I understand you right, you want do the following:
Make an APP which speeks in Thai (Text to speech)
I would use the example I have posted (from Erel).
Question: Isn't there a Thai language set available for Android devices (like German or English here in Europe?)
If not, I would use the English language set and make a simple "translation matrix" (as you did). I don't have any examples for Thai but in German here's an example:
The German word "Kindergarten" (same in English) would be transfered to "Keendergurtaen" (in German we spell the "i" like "ee" in English). So I would send "Keen der gur taen" to the Speech API and the word sounds English.
It's the same in Thai or any other language (assuming we have the English language set only to work with). So you don't need to join MP3's (or even record it)
So there are two ways for you:
1. Get a Thai language set for Android
or
2. use the English set and build a matrix of Thai word -> Phrase with the "sound alike" English phrase.