did you try change font?
go to: data\script\lua
open file: fontdescription.lua in notepad++ or any other txt editor
another thing what you can try is to try change font in bin folder: from webulnw10 to some other take your thai font, rename to webulnw10 and replace in bin folder.
one more thing what you can try to do is try change locale in data\script\localedefine