def set_conversion(self, conversion):
if self.conversion == conversion:<EOL><INDENT>return<EOL><DEDENT>else:<EOL><INDENT>self._dict_init_done = False<EOL>self.conversion = conversion<EOL><DEDENT>
set conversion
:param conversion: the conversion of usage, options are
 'hk2s', 's2hk', 's2t', 's2tw', 's2twp', 't2hk', 't2s', 't2tw', 'tw2s', and 'tw2sp'
 check the json file names in config directory
:return: None