Translator++ would be one of the simpler tools for translating games made in RPG Maker and Ren'Py.
Now I will not say it's the simplest or best however from what I've messed with it, it felt quite easy to use and straightforward for both manual and machine translation.
After translating you simply replace the files that are within GameFolder -> www -> data with the exported translated files and it should work. There should be tutorials out there what to watch out for etc. you just might have to look around or just search for Translator++ where you should be able to find latest version on this website and prob tutorials too.
Edit: Since this was the first time I heard of Treasure Of Nadia I did a quick try and saw that it has a cinematic at start which would be hard to impossible to translate (if there's any others further in the game) without actually editing the I assume video file itself and someone doing voice acting over it. Or possibly just manually adding subtitles to the video.
Translator++ only allows editing what you would see as a text box in the game so everything else would require editing directly at source.