http://en.wikipedia.org/wiki/Gregorian_calendar

Below are the dates when the country switched to the Gregorian Calendar.
Early countries like Italy and Belgium are missing ten days,
late adopters are missing more.

 AL Albania        1912-11-30      IT Italy          1582-10-04
 AT Austria        1583-10-05      JP Japan          1918-12-18
 AU Australia      1752-09-02      LI Lithuania      1918-02-01
 BE Belgium        1582-12-14      LN Latin          9999-05-31
 BG Bulgaria       1916-03-18      LU Luxembourg     1582-12-14
 CA Canada         1752-09-02      LV Latvia         1918-02-01
 CH Switzerland    1655-02-28      NL Netherlands    1582-12-14
 CN China          1911-12-18      NO Norway         1700-02-18
 CZ Czech Republic 1584-01-06      PL Poland         1582-10-04
 DE Germany        1700-02-18      PT Portugal       1582-10-04
 DK Denmark        1700-02-18      RO Romania        1919-03-31
 ES Spain          1582-10-04      RU Russia         1918-01-31
 FI Finland        1753-02-17      SI Slovenia       1919-03-04
 FR France         1582-12-09      SE Sweden         1753-02-17
 GB United Kingdom 1752-09-02      TR Turkey         1926-12-18
 GR Greece         1924-03-09      US United States  1752-09-02
 HU Hungary        1587-10-21      YU Yugoslavia     1919-03-04
 IS Iceland        1700-11-16