every games are different, There are no specified "sound folder".
you will need to examine and understand it yourself.
If you can't even do that, don't think undubing anything by yourself. It may seems an attack, but I'm thinking hacking might be done by people understanding what they are doing.
I'm ok with helping and making tutorials, but I think you are lacking some basics in file system and file format.
Try searching for a game with a folder named "sound", so you couldn't be wrong.
I think you only want to try it and see how it's done, you never mentioned a game in particular, so try with a simple game, with very few audio files.
extract two files, rename it by swapping the filenames, and reinject it into the iso. Burn it, and look if the iso is working, and if the sound is swapped correctly. then do it with japanese audio file into english iso.