The British vs. American English argument is so 1990s. The vast majority of the time an adult Thai today speaks English, they aren't talking to an American or UK national. They're speaking to a Korean or Japanese or a Chinese national.
Consider Spanish and English. Both have a similar number of native speakers. But English has an additional 2 billion people that speak it as a second language - in addition to its 400 million or so native speakers. It’s the only language where the number of non-native speakers dwarf the number of native speakers. And it’s why English is far more important than Mandarin even though that Chinese language has a least twice the number of native speakers.
Ready or not, English is the language of global business.
Consider the example of Rakuten – Japan’s largest online retailer. In 2010, CEO Hiroshi Mikitani, mandated that English would be the company’s official language – a change that effected some 7,100 Japanese employees. His goal was to make Rakuten a top internet services company. And that meant that expansion had to come from outside Japan.
Overnight, the Japanese language cafeteria menus were replaced, as were elevator directories and all other “official” company communications. He stated the employees would have to demonstrate competence in an English scoring system within two years – or risk demotion or even dismissal.
So what happened? Today the “English mandate” has allowed Rakuten to create a much more powerful organization. Three out of the six senior executives in the engineering organization in Tokyo aren’t Japanese as the company aggressively seeks the best talent from around the globe.