You can if you have the Thai garmin map installed.
The only hard restriction I have read on is that the new junction view feature will not install on non Thai firmware (OS) garmin units, I havnt checked the crack forums to see if thats been broken as I dont have a JV supporting unit. Secondly as my reading Thai script is rudimentary at best I am still using transliterated maps which do have the problems you mention (jomtien, chomtien, na chomtien, etc).