Utilities are the exception usually, or something made after someone puts the effort in and possibly translates it.
Anyway PS1 so you need something to pull apart the game into its constituent files... unfortunately Scene standards were not really a thing on the PS1 so there are hundreds of different formats and revisions thereof out there when all the CD writing companies were competing with each other. This also presumes the game does not use raw sector/LBA reads (some games, usually from Square Enix, hid things outside the basic iso 9660 CD format).
Alternatively if you are ripping fresh with current space year technologies then you do have to think what will go when someone grabs a vintage iso.
Anyway plenty of tools that will play here with the custom formats. If going more stock then there are things to rebuild it as well
From here fairly standard find the text, see what characters it supports, maybe edit the font to add/change characters if you need that (not all Japanese games will have a good Roman alphabet in there, and if you want the non English punctuation then almost certainly not going to find it there by default) and also figure out any pointers (games don't know where text starts and ends and it is quite costly to scan a text file every time, to that end files* will have pointers to note where everything is and changing text length necessitates this).
From there you can dump the text, hopefully into something that is reasonable to insert again afterwards.
Various menus, on screen graphics and more might not be simple text but actually graphics and thus need to be edited accordingly.
More advanced stuff might consider then some variable width fonts or other tweaks but that can be left for more advanced things. The PS1 has a fair bit of memory so you probably won't run into memory issues and need to cut down space (or consider an 8 bit conversion) but you never know.
*unlike some cartridge based stuff then files here will typically be loaded into memory so it might be a memory address, especially if it is in the binary, or will possibly be referencing locations within the file itself.