Replace hand-maintained BCP47 table with language-tags

- Drop lib/utils/country-codes.js (628 lines).
- Use language-tags (registry-backed validation via the IANA
  language-subtag-registry transitive dep) instead of a per-subtag
  allowlist; keep the empty/whitespace early-return.
- Pinned to ^1.0.9 (last CJS line; v2.x is ESM).

Behavioral note: language-tags rejects deprecated grandfathered tags
(e.g. `i-klingon`, preferred value `tlh`). The previous hand-rolled
validator also rejected `i-klingon` (its subtags weren't in the table,
nor was the whole tag), so existing tests are unchanged — but consumer
templates relying on deprecated tags would now be flagged.

Author: johanrd

lib/rules/template-require-lang-attribute.js

@@ -1,194 +1,4 @@
-const COUNTRY_CODES = require('../utils/country-codes');
-
-// Common valid BCP 47 primary language subtags (not exhaustive, but covers the most common).
-// Used as a fast-path check for the primary subtag; full validation of every
-// hyphen-separated subtag is performed against COUNTRY_CODES (mirroring
-// ember-template-lint's upstream behavior).
-const COMMON_LANG_CODES = new Set([
-  'aa',
-  'ab',
-  'af',
-  'ak',
-  'am',
-  'an',
-  'ar',
-  'as',
-  'av',
-  'ay',
-  'az',
-  'ba',
-  'be',
-  'bg',
-  'bh',
-  'bi',
-  'bm',
-  'bn',
-  'bo',
-  'br',
-  'bs',
-  'ca',
-  'ce',
-  'ch',
-  'co',
-  'cr',
-  'cs',
-  'cu',
-  'cv',
-  'cy',
-  'da',
-  'de',
-  'dv',
-  'dz',
-  'ee',
-  'el',
-  'en',
-  'eo',
-  'es',
-  'et',
-  'eu',
-  'fa',
-  'ff',
-  'fi',
-  'fj',
-  'fo',
-  'fr',
-  'fy',
-  'ga',
-  'gd',
-  'gl',
-  'gn',
-  'gu',
-  'gv',
-  'ha',
-  'he',
-  'hi',
-  'ho',
-  'hr',
-  'ht',
-  'hu',
-  'hy',
-  'hz',
-  'ia',
-  'id',
-  'ie',
-  'ig',
-  'ii',
-  'ik',
-  'io',
-  'is',
-  'it',
-  'iu',
-  'ja',
-  'jv',
-  'ka',
-  'kg',
-  'ki',
-  'kj',
-  'kk',
-  'kl',
-  'km',
-  'kn',
-  'ko',
-  'kr',
-  'ks',
-  'ku',
-  'kv',
-  'kw',
-  'ky',
-  'la',
-  'lb',
-  'lg',
-  'li',
-  'ln',
-  'lo',
-  'lt',
-  'lu',
-  'lv',
-  'mg',
-  'mh',
-  'mi',
-  'mk',
-  'ml',
-  'mn',
-  'mr',
-  'ms',
-  'mt',
-  'my',
-  'na',
-  'nb',
-  'nd',
-  'ne',
-  'ng',
-  'nl',
-  'nn',
-  'no',
-  'nr',
-  'nv',
-  'ny',
-  'oc',
-  'oj',
-  'om',
-  'or',
-  'os',
-  'pa',
-  'pi',
-  'pl',
-  'ps',
-  'pt',
-  'qu',
-  'rm',
-  'rn',
-  'ro',
-  'ru',
-  'rw',
-  'sa',
-  'sc',
-  'sd',
-  'se',
-  'sg',
-  'si',
-  'sk',
-  'sl',
-  'sm',
-  'sn',
-  'so',
-  'sq',
-  'sr',
-  'ss',
-  'st',
-  'su',
-  'sv',
-  'sw',
-  'ta',
-  'te',
-  'tg',
-  'th',
-  'ti',
-  'tk',
-  'tl',
-  'tn',
-  'to',
-  'tr',
-  'ts',
-  'tt',
-  'tw',
-  'ty',
-  'ug',
-  'uk',
-  'ur',
-  'uz',
-  've',
-  'vi',
-  'vo',
-  'wa',
-  'wo',
-  'xh',
-  'yi',
-  'yo',
-  'za',
-  'zh',
-  'zu',
-]);
+const tags = require('language-tags');
 
 const DEFAULT_CONFIG = {
   validateValues: true,
@@ -198,30 +8,7 @@ function isValidLangTag(value) {
   if (!value || !value.trim()) {
     return false;
   }
-  const normalized = value.trim().toLowerCase();
-  const parts = normalized.split('-');
-
-  // Primary subtag must be a known language code. Keep the original
-  // COMMON_LANG_CODES fast-path so bare tags like "zh" remain valid even
-  // when they are not present in the full country-codes table.
-  if (!COMMON_LANG_CODES.has(parts[0])) {
-    // Fallback: the whole value may be a registered grandfathered/irregular
-    // tag (e.g. "zh-hant", "sgn-gb").
-    return COUNTRY_CODES.includes(normalized);
-  }
-
-  // Validate every remaining hyphen-separated subtag (region / script /
-  // variant) against the full country-codes table, mirroring upstream
-  // ember-template-lint. A whole-string match against COUNTRY_CODES is
-  // also accepted to cover multi-part registered tags.
-  if (parts.length === 1) {
-    return true;
-  }
-
-  return (
-    parts.slice(1).every((p) => COUNTRY_CODES.includes(p)) ||
-    COUNTRY_CODES.includes(normalized)
-  );
+  return tags(value.trim()).valid();
 }
 
 function parseConfig(config) {