IronJovi - This exactly (well, I don't do #3). Even if you use a tool to translate, definitely translate the .js files manually. Some other tips:
4. You should only need to edit
plugins.js as this calls the other scripts.
5. Edit after the : only. The structure is usually "reference on script":"what it displays as"
3. (my version)
I personally edit the .json files directly, as I find it annoying to hunt through the map/menus. You can use the "AnalysePlugin" on Notepad++ to find code 401, 402, 102 which are the most common for displayed text. If I'm really stumped, I'll use FileSeek on the data folder to find the japanese text (how I found the "combat popups"... code 318 or something)