Objects in data dictionary are stored in UNICODE, so if you've got a client app with a font capable of representing the thai symbols, you should be able to create tables with thai-named columns only by double-quoting the names in creation -not tested, i don't know thai ;)-
But I successfully created a table with this:
CREATE TABLE MY_DB."NÚMEROS" ( ID_N INTEGER NOT NULL,
PRIMARY INDEX (ID_N)
BTW: "수" is 'number' in korean.