ISO 639 has three code lists. The following is a complete list of
ISO 639-2 codes, including the corresponding
ISO 639-1 codes where they exist. The codes are sorted by language name in the third column. The
DIS/ISO 639-3 codes are not included.The standard defines some codes for special situations:mis, for "miscellaneous languages";mul, for "multiple languages";und, for "undetermined language";zxx, for "no linguistic content". There is also a range reserved for local use: qaa-qtz.Where two alpha-3 codes are given in the table, the first is the bibliographic code (B code) and the second is the terminological code (T code).
See more at Wikipedia.org...