local-lang-names

Given an ietf-flavored language tag like en-us. It will return the name of the language in the local language, e.g. English (United States). A tag like en will return English.

var langname = require('local-lang-names')

console.log(langname('en-us'))
console.log(langname('de-ch'))
console.log(langname('de'))

Prints

English (United States)
Deutsch (Schweiz)
Deutsch