Self-defense is an accepted defense at trial under Thai law. Sections 67, 68, and 69 of the Thai Criminal Code deal with self-defense, with Section 68 stating "such act is a lawful defense." https://library.siam-legal.com/thai-law/criminal-code-criminal-liability-sections-66-72/
Unfortunately the unofficial English translation of the Thai Criminal Code is very clumsy with some laughable mistakes, i. e., what should be "guilt" or even better "guilty" is given as "quilt."
The Thai laws on self-defense are similar to English common law and modern U.K. criminal law. The test in both countries is that acts taken in defense against imminent danger are "reasonable" and "proportionate." This is different from the U.S., where 11 states mandate a "duty to retreat" before deadly force can be used in self-defense; 38 have "stand your ground" laws which don't require an attempt to retreat; and one state and the District of Columbia have a "mixed" law, with a duty to retreat under some circumstances and stand your ground under others.