Improve the quality of Thai English teachers. Teachers of English have to be an inspiration for their students. It should be natural for young Thai students to say “If my teacher can do it, I can do it too.” A white native speaker from Texas without a degree in English literature can never be an inspiration for Thai students.
If Thailand really wants to employ foreign teachers, then they must be qualified language teachers, not just native speakers. They have to be trained in language or linguistics and speak at least one or more foreign languages.