WARNING: This trick will potentially delete your saved data. Only do it if you are willing to accept the consequences. Some gamers have reported serious malfunctions due to this trick. Unless You REALLY need some entertainment DON'T DO IT! Also you should save your game to a memory card.

In order to do this, go to the name-select screen and start a new game. Once the page comes up (where you choose your letters) gently and slowly lift up on the left side of your game pak, until the sound is slightly obscured. Now, with the game pak still ajar, select any name you desire and enter it in.
After this is done, hit "end" and gently push your game pak back into the n64 console. Then shut off your n64 and start it up again ... ... If you followed the directions right then the next time you go to the name-select screen all of the text will be written in Japanese. The strangest thing though, is that if you start a game (one that was saved in the past), the in-game text will still be in English! Though, when it comes to the newly saved game, if you start it up again it will almost immediately freeze on you. Also, Note: If you do not want your names to remain in Japanese, then don't try this trick!
The only way to change the names back to English is by erasing the saved games and starting them over. Well, I hope you all enjoy this new trick!!!