As you see, language files are JSON files which means you can work around with object (that's why your lang file starts with { and ends with }) and sub objects
About best practice and keys in json files, I don't know, but I've seen two version (we're mainly using 1st one):
en.json
{
"NEWS": "News",
"NEWS_NO_DATA": "No data for News page",
"NEWS_FETCHING": "Fetching news from server..."
"ABOUT": "About",
"ABOUT_LICENCE_AGREEMENT": "I'm kidding",
"ABOUT_EMAIL": "..."
}
or option 2:
en.json
{
"NEWS": {
"TITLE: "News",
"NO_DATA": "No data for News page",
"FETCHING": "Fetching news from server..."
},
"ABOUT": {
"TITLE: "About",
"LICENCE_AGREEMENT": "I'm kidding",
"EMAIL": "..."
}
}