Yes, Bitcoin trading is legal in Thailand. The Thai Securities and Exchange Commission has released a statement saying that they consider Bitcoin and other digital currencies to be commodities and not securities. This means that Bitcoin trading falls under the existing lAWS for commodities trading in Thailand. There are no specific lAWS or regulations pertaining to Bitcoin trading in Thailand at this time.
However, the Thai government has been working on drafting regulations for the cryptocurrency industry. It is expected that these regulations will be released sometime in 2018. Until then, Bitcoin trading remains legal in Thailand.