The Budokai series (or Dragonball Z 1 - 3 in Japan) was aquisitioned by Atari (Formerly, Infogames) to be made as a PS2 fighter. DIMPS, a Japanese Company took the helm. Since it was intended for the american market initially, it Came out here first. Budokai 1 was a Smash hit! not only here but in Japan! and when it came time for B2 to come out, it was initially intended to have a joint release in both countries. however, They decided to stuff some cool extras in the Japanese version, such as Freeza's son Kuriza being a playable Character in the form of Freeza's 4th Costume and a Whole new level for Dragon World based on Neko Majin Z, a Dragonball Parody manga by toriyama himself!
them Budokai 3 came time to come out and This time, the game had a far rushed release, this can be seen in the games files as it includes voice Options for MULTIPLE characters who dont appear in the game. including BURUMA!! ("Bulma" in america) so then the Japanese Version came out later and included a MUCH better boxart, a vocal Version for the opening theme (as did B2) and a Plethora of new Extras, including a Halo and Wings Costume for Goku, Trunk's Saiyajin Armor, and Piccollo Daimao as Piccollo's costume! not only that, but Buruma is Actually Playable in the form of and extra costume for Videl. How to unlock this I dont know but I believe a gameshark may be needed.
Then, Bandai Decided to aqisition their own Dragonball Game from Developer SPIKE. The Game Was to feature a TON of characters and would be called "Dragonball Z: SPARKING!" Sparking Cameout in Japan First and Was not as good As DBZ3 but was still fun. It included Actual Music from the Series! then it came out in america, the Music was changed to a recycled mix of Budokai 1-3 Music, and surprisingly, this was the first Dragonball Game to have JAPANESE VOICES SELECTABLE!!! however, they attempted to Make it seem like it was part of the Budokai series by grossly incaurately Naming it "Budokai Tenkaichi" which is obviously supposed to be "Tenkaichi Budokai" but they wanted the word "Budokai" there first to show its involvement in the series, despite its RADICALLY different Engine and removal of the Transformations. I get quite mad when it's reffered to as Budokai Tenkaichi or Budokai anything. Because it ISNT a Budokai game.
Nevertheless, Japan usually took longer to realse it because they wanted to ADD things