A portion of a Wired interview with J-Pop star, Tsunku♂...

Wired.com: Tell me about the process of localizing Rhythm Heaven for an English-speaking audience. Many of the songs had to be changed. Were you involved in this process? What was the most challenging part of the game to localize?

Tsunku♂: I mainly work in producing and writing J-pop songs, but unfortunately, because the songs are in Japanese, even if an album sells 2 million copies in Japan, it would never make it to America. And that's why the Grammys have never come calling [laughs].... Rhythm games have always transcended nationality, though. Rhythm is something that can be learned without complex theories; it just takes practice and repetition. This is true for children, adults, men and women. This is why I thought a worldwide release of this title wasn't just a pipe dream.

As for the changes to song lyrics in the American version, the staff in Japan translated the songs into English, staying as close as they could to the meaning of the Japanese. Then the staff at Nintendo of America localized them for an American audience, and the lyrics as they are now were completed. Our main concern, though, was maintaining the flow and emphasis in the songs that enable all of the game's tapping and button-pressing. There would be no point in the game if we sacrificed the rhythmic gameplay just to make the meaning of the English and Japanese lyrics match, so we had the localizers take extra care with this.

Full interview here