Most Deaf Thais use TSL but there are slight variants in the different regions, it's not a big difference tho. It's similar to here in the US, we live in the Midwest and when I interpret for a Deaf person from NY they will totally understand me even if it is something really complicated like bypass surgery.

When you get outside of thailand, the language totally changes. The Thai and Malay would understand each other just on a superficial level with just some basic signs being similar. I hope that makes sense.