There is now a confirmed release date for the Japanese release of Final Fantasy VII: Advent Children. North America / United States and European/ UK release is still unconfirmed. Please read below for the Advent Children release date.

Japanese flag – 14th September, 2005
USA flag – Late 2005 / Early 2006 (unconfirmed)
European flag – Late 2005 / Early 2006 (unconfirmed)