What time of year are you looking at going? How long are you going for? Are you only wanting to train MT or do you want to see the country too?
Thailand is hot. Especially in the summer it can still be in the upper 90s F at night-time. Personally, I think the best time to explore any part of Thailand is the winter. The weather is much more agreeable. If you go to Northern Thailand, such as Chiang Mai, it actually sits at a bit of altitude and is typically 5 - 10 degrees cooler. In Southern Thailand, like where Drop Bear mentioned, you will see a lot of Malay influence... in the speech, food, and culture. The three most southern provinces of Thailand you shouldn't go to. There have been more roadside bombs than Afghanistan and Iraq combined as it was originally its own nation that was given to Thailand by the British roughly 100 years ago. 30 or so years ago a strong resistance movement formed. Likewise, if you go to Northern Thailand, you will see a lot of Laotian influence. Thai and Laotian are already very close languages (think Portuguese and Spanish) but in that area, Isaan, its blended even more. Overall, it's a very tourist friendly country and you can always find English speaking folks to point you in the right direction.