Thailand have not always celebrated the Julian calenders New Year, it used to be according to the Buddhist calender where the year change in differently.
As I have understood it the king changed it to follow the rest of the world because it was causing to much misunderstandings as Thailand became more and more involved with the greater world.
Also our New Year this night will change from 2560 to 2561.
Hope that some like my post and best greetings for the holidays and new year from Thailand.