RTAF is third Southeast Asian Air Force to select KAI T-50

Thailand has signed a contract with Korea Aerospace Industries (KAI) for four T-50 advanced jet trainers.

By 대한민국 국군 Republic of Korea Armed Forces (국산 초음속고등훈련기 T-50) [CC BY-SA 2.0], via Wikimedia Commons

The signing ceremony took place at the JW Marriott Hotel in Seoul. KAI has 30 months to deliver those jets.
Indonesia is the first country in Southeast Asia to operate the T-50. Philippines was next and the country is expecting the delivery of its first jet this year.
Of note, this is the first time the M-346 lost to the T-50 in a competition.

Source: RTAF is third Southeast Asian Air Force to select KAI T-50