Being able to speak Thai is irrelevant in a multi-lingual class, which you'll get if you teach in an international school or a language institute. Even in a Thai school there should be a Thai assistant, so the foreign teacher being able to speak Thai (badly!) is more of a hindrance than a help.
Yes, assuming you mean TEFL. However here more emphasis is placed on having a degree (for the WP). TEFL in Europe and most other Asian countries place the emphasis on having a decent TEFL/TESOL qualification like a CELTA or Trinity.
The UK really have things screwed up! You can't travel to a country with virtually no Covid, yet kids can go to school and people can go to work on crowded public transport!