1. A method of encoding a data string into a bar code symbol, the data string comprising a plurality of data characters, the data characters selected from a double byte character set of human readable characters, a number of the data characters also being contained in a single byte character set which is a subset of the double byte character set, the method comprising the steps of: determining a plurality of character codes corresponding to the plurality of data characters, the character codes selected from a first set of character codes, the first set of character codes being mapped to the first set of data characters; parsing the data string to separate the double byte character codes of characters from the single byte character set from the data string; converting the double byte character codes in the parsed data string into double byte symbol values; converting the double byte character codes parsed from the data string into single byte symbol values; and outputting the double byte symbol values and the single byte symbol values to form the bar code symbol.