.Arc Files?

I posted this in here because I am currently working on a game translation and I need some help. I was trying to avoid writing a patch for the game and just hoping to edit the script into English tho I have not been able to find it and I have 3 files yet to open. A 550mb file, a 350mb and a 3mb file all in Arc Format. I can open the 3mb one in notepad without it crashing and it seems it is all coded but there is some Japaneses in there which seems like script (to an extent).
I am posting this to see if anyone knows how to open an Arc file so I can view the other files to see if I can make any leeway.
Or if anyone has previously translated a game, can they tell me if it would be better to write a patch.

Thanks.