Just tried the following process on my Japanese copy - worked fine - plus once you have the text in English, you can see an option for the voices to be in English too...
(from
https://iwasateenagepcenginefan.wordpress.com/2011/02/16/so-uh-how-do-i-play-j-b-harold-murder-club-in-english/ )
1) Start the game. You’re at the screen where the woman says, “Hi, JB!” Press Button I to bring up a menu with five commands.
2) You want NONE of those commands. Press right on the D-pad to get to a sixth command. Select this one.
3) Now you’re at a screen with a gun. Press button I to bring up a menu with five commands.
4) You want NONE of those commands. Press right on the D-pad to get to two more commands. Select the top one.
5) Two more commands come up. Pick the bottom one.
6) The menu disappears. Press button I to bring it up again and voila! English text.