Basically.... and obviously, the next movie is based on Celebi. I think people already know that much.
The title of the movie will be "Celebi A Timelss Encounter". Too hokey sounding in English, the movie will most likely be renamed to something better like "Pokémon the 4th Movie" (notice the subtle hint of sarcasm there?). Actually, it'd be something more along the original Japanese title, just less hokey sounding.
This here is a press conferece of some sort... which happened back on November 30th I believe. Not much is actually said about what actually went on there though... sna.
Anyway.... also included on the movie info page was a quick little summary of the main feature, and the side cutesy fun flick for the kids. The translations were a lot a bit patchy, so I'll see about trying to reconstruct it as best as possible.
The Ilex Forest is one of the largest forest found in Johto. Inside it is a great river, flowing with the purest of water. ... In the forest, legend has it that there is a voice so powerful, it can make the rivers stop flowing.
The legend comes true when a local boy, Yukinari, hears it as he enters the Ilex Forest. It speaks to him saying: "The protector of the forest, who has power over all time, can be seen by a kind-hearted boy...." For one second, Yukinari does see Celebi, the forest's protector, and is taken in it's beauty...
... 40 yers later... Ash and Company reach the Ilex Forest. In it, the crew meet up with and older Yukinari, and easily befriend him. Later, they meet Bishasu, a selfish Pokémon trainer, who's ultimate goal is to capture Celebi. In an effort to prevent Bishasu's dirty plan, a large scale battle begins between Ash and Bishasu.
Soon enough... Celebi reveals itself in a final showdown...
Ash and company reach a Seaside city in the western part of Johto. In it, there is a beautiful garden with all sorts of flowers. Pikachu and the rest of the Pokémon decide to check it out and have some fun in the mean time.
However, Larvitar (apparently a new Pokémon of Ash's or something, -Nick15) is not all that interested with playing in the garden, and decides to wander off. Accidently, Lavitar turns on a lawn mower, which poses a serious threat to the garden!
(Nick15's Note: Bleck... more little kiddy fun here.)
Yep, those are the movies for you. Good times...
OK well, that's it for me then. That's all the info I bothered to translate. ;)