If you say 'the files' do I understand that as all the files because if so that is probably an archive format and will probably contain all sorts of things. On top of this the visual novel format lends itself to being part of a complete scripting engine quite well (or at the very least something in the linked list family) and with them tending not to make it outside Japan the programmers of them quite often do not make translation (either ones where people might have source code or unofficial like this hence they the can be difficult comment). The basic principles of translating a PC game and translating a console game are the same (find the text, find how it is encoded, find out how any markup and/or pointers for it works and go nuts) but PC games can and do frequently use lots of compression (Japanese programmers favour some odd methods there but Japanese computing in general seems to favour odd methods), encryption (usually something very basic like a weak XOR and unlikely to stand up to any real attack but still encryption) and can still store all their text as images in the game rather than just use a font instead (nice as you can never be sure what a system will have).

Persona opera za no kaijin screenshots