Cyrille

Dude - it can't be ignored that the standard of English in Thailand is lower than in many other areas of the region.

I think the major reasons are:

1) It's so completely different from their first language.
2) Thais are often very self conscious, and prefer to avoid what may be seen as 'drawing attention to themselves' by communicating well in English.
3) People can be really, really withering in a subtle way to those who do 'draw attention to themselves' by communicating well in English.
4) The frequent absence of anything at all even resembling study skills.
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I don't go along with the two reasons put forward by the op! I don't believe there is significantly more xenophobia or less intelligence amongst Thais than you'll find anywhere else in the region.