I found unused english strings in the Kao 3 install, and managed to get them switched around and loading. There's some grammatical issues and so on which I have not fixed, as I am not sure what will cause them to display improperly or not, but the game is now fully playable in English. It's also not very good, but whatever!
http://www.4shared.com/file/L2AHHyh9ce/lang_psp.html
simply put this in the media/misc/localize folder in your install and overwrite the original!