Interesting. I am not even sure if this is a valid regex, as I am not sure if the "-" character is allowed in the position that it is in. And if it is allowed, then I am still not sure if it is valid, as there may be an extra "]" remaining. Perhaps, someone better with regular expressions can shine a better light here.
In the meantime, can you tell us what you think that this regex is supposed to do?
Oh, I see. The "-" character, in that position, is a subtraction operator. Interesting.
That site also answers your question -- it is a character in the character set of Thai characters.
And BTW, the current Java regex engine does not support the subtraction operator. It also does not support the Thai character set.... so, basically, that regex is invalid when using the current Java regex engine.