To add new language to the game you’ll need:

• assets/options.json
• assets/texts/lang_*your-lang-code*.json

1. In the options file find the “languages” key, and add the new language code: 

"your_lang_code": { "name": "lang_translation_key" }

2. Create a new file in assets/texts/ with the name lang_*your_lang_code*.json, put the data from lang_en and you can start translating the game to the new language.