Definitely NOT change the script!
The mistranslations have a very special charm, and changing them would rob FF7 of a lot of its personality.

"Attack while it's tail's up! It's gonna counter-attack with its laser!"
"This guy are sick."
"Hmmmmm, that's how you'll fool them. Hmmmmmm, so that's how you fooled them."
"Poo, I, uh, mean, this way, sir..."
"Off course! No, way!"

Do we really wanna change these lines?
They rock!

I would probably change the amount of missable items in the game, because I always hated missable items.