How Do I Type in Japanese on PS3

[HEC]

I play in English but I would like to type in Japanese to my friends but I'm not sure how I can switch without possibly changing the entire language setting to Japanese.

Press tilda (~) or ¬ key (left of 1 on top row / bellow ESC key on standard keyboard) to switch between Japanese and normal character entry in the chat log if that's what you were asking about. Press again to switch back.