What countries have Bilateral Tax Agreement with Thailand?
Bilateral Tax Agreement is only effective with income Tax, which in Thailand covers Capital Gain Tax. To avoid income to be taxed on twice from two countries due to Residence Rule and Source Rule, Thailand has Double Taxation Agreement with following countries;

Norway, Denmark, German, France, Singapore, Netherlands, South Korea, Italy, Belgium, Pakistan, Britain and North Ireland, Indonesia, Malaysia, Philippines, Poland, Canada, Austria, Finland, India, Republic of China, Hungary, Japan, Australia, Sweden, Sri Lanka, Vietnam, Czechoslovakia, Israel, South Africa, Switzerland, Romania, United State, Laos, Moriches, Luxemburg, Bangladesh, Nepal, Spain, New Zealand, Uzbekistan