Why learn Thai?
Well, actually, you don’t need to learn Thai at all!
There are enough people who can speak or understand English – even (or especially) in business – that you can get by and live quite successfully in Thailand… for many years. Some expats have been here for 10 or 15 years and own or manage successful businesses, without speaking more than a smattering of Thai.
Besides, Thai is quite difficult and boring to learn – that is, if you go to a ‘traditional’ class or try to learn it the way it is conventionally taught.