Google Translate has an English to Thai interface with speech.
Now off to the more pressing question. I was able to get it to work on my N7. This may be a silly question, but is your volume level up? I know that I customarily keep mine silent, so it is easy for me to overlook, then bang my head against the wall looking for something else.
The speaker icon was grayed out, although, I made sure the language I wanted to hear, in my case, Latin, was on the top of the two lists of texts. My best piece of advice is to either mess around with what language is on top, and if you still have issues, I would delete the application, restart the device, then reinstall it again. As I have found over the years, apps get buggy, and sometimes you just have to dump it, then start fresh. Please repost your findings, so that if neither work, I can look a bit closer.