Although I've known about the hidden Excel function BahtText for some
time, I've just discovered some other Thai functions when browsing the
hidden members of the WOrksheetFunction object in the object explorer:

IsThaiDigit
RoundBahtDown
RoundBahtUp
ThaiDayOfWeek
ThaiDigit
ThaiMonthOfYear
ThaiNumSound
ThaiNumString
ThaiStringLength
ThaiYear