Regular expressions for matching IETF language tags (BCP 47)

Based on this Stack Overflow comment by George Pollard.

const languageTagRegex = require('ietf-language-tag-regex')

languageTagRegex().test('en-GB')   // true
languageTagRegex().test('a-DE')    // false
languageTagRegex().test('zh-Hant') // true

Returns a regex for matching IETF language tags.

Type: boolean
Default: true

Only match an exact string. Useful with RegExp#test to check if a string is a language tag.