i18n(ar): register Arabic as the first right-to-left language

- Add ar to LOCALES (picker name العربية) and RTL_LOCALES, so <html dir>
  turns rtl; any ar-* tag maps to it.
- Intl formatters get ar-u-nu-latn: numbers and dates keep Western digits
  like the catalog, whatever the browser's ICU picks for Arabic regions.
- HUD quantities keep a space before an Arabic unit (2069.0 كم), as in
  Chinese, instead of running digits into the word.
- Codes and product names that stay Latin go to same-as-english.json.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/i18n/ar-display.test.mjs

@@ -0,0 +1,101 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { formatDate, formatNumber, getLocale, setLocale, t, tn } from './index.js';
+import {
+  applyDocumentLanguage,
+  intlLocale,
+  LOCALE_STORAGE_KEY,
+  resolveLocale,
+} from './locale.js';
+import { hudQuantity, LOCALIZED_LOCALITY } from '../hudLocalityFormat.js';
+import { formatCockpitDistance } from '../ui/cockpitPresentation.js';
+import { READOUT_WORDS } from '../layers/recentImagery/display.js';
+
+test('Arabic resolves from URL, saved preference and browser language', () => {
+  assert.equal(
+    resolveLocale({
+      location: { search: '?lang=ar-EG' },
+      storage: { getItem: () => 'en' },
+      languages: ['en'],
+    }),
+    'ar',
+  );
+  assert.equal(
+    resolveLocale({
+      location: { search: '' },
+      storage: {
+        getItem: (key) => (key === LOCALE_STORAGE_KEY ? 'ar' : null),
+      },
+      languages: ['en'],
+    }),
+    'ar',
+  );
+  assert.equal(
+    resolveLocale({
+      location: { search: '' },
+      storage: { getItem: () => null },
+      languages: ['ar-SA', 'en'],
+    }),
+    'ar',
+  );
+});
+
+test('Arabic turns the page right-to-left; other languages stay left-to-right', () => {
+  const doc = { documentElement: {} };
+  applyDocumentLanguage(doc, 'ar');
+  assert.deepEqual(doc.documentElement, { lang: 'ar', dir: 'rtl' });
+  applyDocumentLanguage(doc, 'zh-CN');
+  assert.deepEqual(doc.documentElement, { lang: 'zh-CN', dir: 'ltr' });
+});
+
+test('Arabic formats with Western digits whatever ICU defaults to', () => {
+  assert.equal(intlLocale('ar'), 'ar-u-nu-latn');
+  assert.equal(intlLocale('ru'), 'ru');
+  const previous = getLocale();
+  try {
+    setLocale('ar');
+    assert.equal(formatNumber(1234.5), '1,234.5');
+    assert.equal(
+      formatDate(Date.UTC(2026, 7, 26), {
+        day: 'numeric',
+        month: 'long',
+        year: 'numeric',
+        timeZone: 'UTC',
+      }),
+      '26 أغسطس 2026',
+    );
+    assert.doesNotMatch(formatNumber(9876543210), /[٠-٩]/);
+  } finally {
+    setLocale(previous);
+  }
+});
+
+test('Arabic uses all six plural forms and spaced HUD units', () => {
+  const previous = getLocale();
+  try {
+    setLocale('ar');
+    assert.deepEqual(
+      [0, 1, 2, 3, 11, 100].map((n) =>
+        tn(n, '{count} SOURCE', '{count} SOURCES'),
+      ),
+      [
+        '0 مصدر',
+        'مصدر واحد (1)',
+        'مصدران (2)',
+        '3 مصادر',
+        '11 مصدرًا',
+        '100 مصدر',
+      ],
+    );
+    assert.equal(hudQuantity(2069, 'km', 1), '2069.0 كم');
+    assert.equal(formatCockpitDistance(14000), '14 كم');
+    assert.equal(
+      LOCALIZED_LOCALITY.sector({ latDeg: 21.33, lonDeg: -77.5 }),
+      'القطاع 21.33ش 77.50غ',
+    );
+    assert.equal(READOUT_WORDS.daysAgo(9), 'قبل 9 أيام');
+    assert.equal(t('SAVE KEYS'), 'حفظ المفاتيح');
+  } finally {
+    setLocale(previous);
+  }
+});

src/i18n/i18n.test.mjs

@@ -47,6 +47,9 @@ test('normalizeLocale folds regional variants and rejects unshipped tags', () =>
   assert.equal(normalizeLocale('zh-Hant-CN'), 'zh-Hant');
   assert.equal(normalizeLocale('zh_HK'), 'zh-Hant');
   assert.equal(normalizeLocale('zh-MO'), 'zh-Hant');
+  assert.equal(normalizeLocale('ar'), 'ar');
+  assert.equal(normalizeLocale('ar-EG'), 'ar');
+  assert.equal(normalizeLocale(' AR_sa '), 'ar');
   assert.equal(normalizeLocale(undefined), null);
 });
 
@@ -102,6 +105,10 @@ test('applyDocumentLanguage sets lang and dir', () => {
   const doc = { documentElement: {} };
   applyDocumentLanguage(doc, 'ru-RU');
   assert.deepEqual(doc.documentElement, { lang: 'ru', dir: 'ltr' });
+  applyDocumentLanguage(doc, 'ar-EG');
+  assert.deepEqual(doc.documentElement, { lang: 'ar', dir: 'rtl' });
+  applyDocumentLanguage(doc, 'en');
+  assert.deepEqual(doc.documentElement, { lang: 'en', dir: 'ltr' });
 });
 
 test('t() returns English text in English and translates in Russian', () => {

src/i18n/index.js

@@ -13,15 +13,23 @@
 // `npm run i18n` keeps the catalogs in step with the code. Guide: docs/I18N.md.
 import {
   DEFAULT_LOCALE,
+  intlLocale,
   normalizeLocale,
   writeStoredLocale,
 } from './locale.js';
+import ar from './locales/ar.json' with { type: 'json' };
 import es from './locales/es.json' with { type: 'json' };
 import ru from './locales/ru.json' with { type: 'json' };
 import zhCN from './locales/zh-CN.json' with { type: 'json' };
 import zhHant from './locales/zh-Hant.json' with { type: 'json' };
 
-const CATALOGS = Object.freeze({ es, ru, 'zh-CN': zhCN, 'zh-Hant': zhHant });
+const CATALOGS = Object.freeze({
+  ar,
+  es,
+  ru,
+  'zh-CN': zhCN,
+  'zh-Hant': zhHant,
+});
 
 let currentLocale = DEFAULT_LOCALE;
 
@@ -157,7 +165,7 @@ function cachedFormatter(kind, Constructor, options) {
   const cacheKey = `${kind}|${currentLocale}|${options ? JSON.stringify(options) : ''}`;
   let formatter = formatterCache.get(cacheKey);
   if (!formatter) {
-    formatter = new Constructor(currentLocale, options);
+    formatter = new Constructor(intlLocale(currentLocale), options);
     formatterCache.set(cacheKey, formatter);
   }
   return formatter;

src/i18n/locale.js

@@ -8,11 +8,19 @@ export const LOCALE_STORAGE_KEY = 'gev:locale:v1';
 export const DEFAULT_LOCALE = 'en';
 
 /** Shipped locales; order does not matter. Adding one: docs/TRANSLATORS.md. */
-export const LOCALES = Object.freeze(['en', 'es', 'ru', 'zh-CN', 'zh-Hant']);
+export const LOCALES = Object.freeze([
+  'en',
+  'ar',
+  'es',
+  'ru',
+  'zh-CN',
+  'zh-Hant',
+]);
 
 /** Each locale named in its own language, for the selector. */
 export const LOCALE_NAMES = Object.freeze({
   en: 'English',
+  ar: 'العربية',
   es: 'Español',
   ru: 'Русский',
   'zh-CN': '中文（简体）',
@@ -20,10 +28,24 @@ export const LOCALE_NAMES = Object.freeze({
 });
 
 /** Right-to-left locales. */
-const RTL_LOCALES = Object.freeze([]);
+const RTL_LOCALES = Object.freeze(['ar']);
+
+/**
+ * Tags for Intl formatters where the locale code alone is not enough. Arabic
+ * keeps Western digits (0–9) like its catalog: ICU picks Arabic-Indic digits
+ * (٠–٩) for some Arabic regions and browsers, and a HUD that mixes both
+ * misreads.
+ */
+const INTL_TAGS = Object.freeze({ ar: 'ar-u-nu-latn' });
+
+/** The tag to hand Intl.NumberFormat, DateTimeFormat and the like. */
+export function intlLocale(locale) {
+  return INTL_TAGS[locale] ?? locale;
+}
 
 /**
  * Map any language tag to a shipped locale: 'ru-RU' and 'RU' → 'ru',
+ * 'ar-EG' and 'ar-SA' → 'ar',
  * 'zh', 'zh-CN' and 'zh-Hans-SG' → 'zh-CN';
  * 'zh-Hant', 'zh-TW', 'zh-HK' and 'zh-MO' → 'zh-Hant'.
  * @returns {string|null}

src/i18n/same-as-english.json

@@ -1,4 +1,38 @@
 {
+  "ar": [
+    "1090 MHz",
+    "978 MHz UAT",
+    "AIS: --",
+    "AIS: {name}",
+    "BRG {value}°",
+    "BRG —",
+    "CAL {value}",
+    "CAL · {badge}",
+    "CCTV",
+    "CRS {value}°",
+    "CRT",
+    "FLIR",
+    "FOV",
+    "FOV {value}°",
+    "GEO",
+    "GOOGLE STREET VIEW",
+    "Google Street View",
+    "HDG",
+    "HDG {value}°",
+    "Ironbow",
+    "Landsat 8/9",
+    "NVG",
+    "REC",
+    "S2 GhostMaps",
+    "SQUAWK {code} · {status}",
+    "SRC {value}",
+    "Sentinel-2",
+    "WHOT/BHOT",
+    "dB",
+    "hPa",
+    "{source} HTTP {status}",
+    "▲ {frp} MW"
+  ],
   "es": [
     "1090 MHz",
     "978 MHz UAT",