lang_*.json

Language keys file, it simply contains structure of translation words:

KEY:VALUE

{
"language.key": "Language key",
"apple.name": "Apple",
"banana_description": "Banana is very delicious!"
}

As you see, key can be any type of word.

You can use bbcodes in the texts like [b]text[/b] to make text bold, colorize text by [color=hex]text[/color] or [color=red]text[/color], also you can use special bbcodes like [lang]lang.key.code[/lang] - it translates this word from current *_lang, useful for NPC names etc. Also it can translate keyboard keycode of some action and show it's keyboard key - [key_action]action_id[/key_action] this id's can be found in options.json