PS1/2 Anyone knows how to open / extracts these files?

[Sindikvil]

Hello.

I made an account here because for a while now I have been interested in somehow being able to play Dirge of Cerberus with Japanese voices and English text,

I own original copy of Japanese version, together with its iso file, as well as isos for PAL, and International version.

From what I know, there are already more than several Japanese games that had their original audio restored by hobbysts, and well, that in most cases it isn't just about replacing audio files, and call it a day.

I wonder if any of you have some experience with this, or if you know someone that I could contact to help me with this, or if someone smarter than me would be willing to do it.

Here are screenshots:

 

[Sindikvil]

I guess no one...

 

[FAST6191]

By and large you get to help yourself in these sorts of scenarios. Being a Final Fantasy series game (albeit a less than stellar one that never got the greatest fanbase) then you might be more lucky than were you a fan of some random kids anime game that was also awful. You could poke around whatever goes for the Final Fantasy or maybe Final Fantasy 7 hacking communities these days (they are not quite as cohesive or active as they once might have been but there are some) and seeing if they also know something there.

Most undubs with anything using a file system (so things based on floppy discs, optical media or DS or later) are a matter of find relevant files, overwrite accordingly.
Sometimes things will be lost (voicework in Japan, kind of expected, voicework outside it, kind of expensive and also a minor perk at best for most) but things are rarely reshuffled and thus copy-paste works. In those cases where things are lost it tends to make more sense to backport the script to the language you want, though some will try to add it back in (sometimes it is still largely there but doing nothing).

Square(Enix) games on the PS1 and PS2 do tend to be one of the more tricky cases. In this case they seemingly don't care for having people rip audio and thus have been known to stick it in exotic places in the ISO.

To that end you can try yourself if you want. Audio tends to be larger in file size but not as much as video. There might be nice names you can look at (rarely will game devs use obtuse or misleading names, and can eliminate things -- words to do with graphics probably mean graphics contained within). Extensions and magic stamps (open a file in a hex editor and compare against the likes of http://wiki.multimedia.cx/index.php?title=Category:Game_Formats http://wiki.xentax.com/index.php/Game_File_Format_Central for little runs of hex or text that indicate an audio format), the game itself might say something (if a game says criware or rad bink then it probably will be using https://www.criware.com/en/products/adx2.html http://www.radgametools.com/binkgames.htm ). You can try replacing files with others, comparing files between versions of the game (text and graphics featuring text might change but little else graphically will, levels might well be the same...) and this extends to swapping them around and seeing what happens or corrupting them and seeing what happens -- sucks when you are burning discs but today if we have emulators (you only need it to run, not be playable for fun purposes) and USB options...
Ultimately you might have to play big boy debugger and that is a skillset but there is plenty you can do before then, even if it maybe not as accurate and a bit more long winded.