Japanese Visual Novel- technical question =

Hey guys
I wanted to ask if anyone of you knows what to technically do when trying to translate a japanese visual novel (like lamento or omerta) ?
I wanted to get better at japanese and I'm currently at a level where I can translate (easy) manga so I wanted to make a longer project by translating a monstrosity like those visual novel games. The problem is, that I don't know what to do with my translation or how to switch it with the japanese text... Does anyone of you know? Or maybe someone who already has done something like this?