The menus are all in English, and the only parts of the game that require you to know Japanese are some of the onscreen text and the spoken dialogue in the cutscenes. But even then, the story here isn't so complex that you won't be able to put two and two together, whether you've played the original game or not.
For those new to the world of talking dogs and guitar-toting superheroes, there's a full tutorial that you have to play through when you begin a single-player game. There's a lot of text and spoken dialogue here, but all you need to do is look at the animated icons to know what to do. You simply have to move the analog stick and press the face buttons in time with the icons on screen, which are the same in the Japanese and the US versions of the game.