http://moetoku.sakura.ne.jp/gsq2/manual.html
http://store.steampowered.com/app/806720/
Copy jpn.json to a new file for your language, e.g. eng.json, and translate the strings on the right-hand side.
e.g.
"設定.Caption": "Settings", // <- thisPlace the file into the gsq2_Data/StreamingAssets/ directory of GensoYonbaiKen2.
The game contains language.txt. Open it.
And replace jpn with your language. e.g. eng
Start the game, it will render your translations.
And create pull request!