i18n(ja): ship Japanese

- Register ja: CATALOGS, LOCALES, LOCALE_NAMES (日本語) and the package
  boundaries; ja and ja-JP tags select it.
- Japanese unit words follow the number directly, as in the catalog:
  formatQuantity writes 5分 and 1時間5分 (km and kt keep the space), and
  formatRelativeTime drops the space CLDR puts in 5 分前.
- Tests: locale tags, picker order, Intl output, durations and the
  ramp/exit/lane wording in Japanese.
- docs/translations/ja.md: style, units, plurals and glossary; ja added to
  TRANSLATORS.md and CURRENT-STATE.md.

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

src/data/directions.test.mjs

@@ -875,6 +875,13 @@ test('route numbers follow the page language and never break from their unit', (
   );
   const list = directionsStepList({ route });
   assert.equal(list.items[1].lead, '240\u00a0м');
+
+  // Japanese unit words follow the number: 1時間5分, but 1.5 km.
+  setLocale('ja');
+  assert.equal(routeDistanceText(1500), '1.5\u00a0km');
+  assert.equal(routeDurationText(39), '39秒');
+  assert.equal(routeDurationText(3900), '1時間5分');
+  assert.equal(routeDurationText(7200), '2時間');
 });
 
 test('ramp and lane wording stays localized after choosing the maneuver form', (t) => {
@@ -892,6 +899,12 @@ test('ramp and lane wording stays localized after choosing the maneuver form', (
       'Toma la salida bruscamente a la derecha',
       'Toma el carril izquierdo',
     ],
+    [
+      'ja',
+      'ランプを斜め左に進んでI-95に入る',
+      '出口を急角度で右に出る',
+      '左車線を通行',
+    ],
     [
       'zh-CN',
       '向左前方驶入匝道，进入 I-95',

src/i18n/i18n.test.mjs

@@ -5,6 +5,7 @@ import {
   applyDocumentTranslations,
   formatDate,
   formatNumber,
+  formatRelativeTime,
   msg,
   persistLocaleAndReload,
   setLocale,
@@ -35,6 +36,9 @@ test('normalizeLocale folds regional variants and rejects unshipped tags', () =>
   assert.equal(normalizeLocale(' RU '), 'ru');
   assert.equal(normalizeLocale('en_GB'), 'en');
   assert.equal(normalizeLocale('xx'), null);
+  assert.equal(normalizeLocale('ja'), 'ja');
+  assert.equal(normalizeLocale('ja-JP'), 'ja');
+  assert.equal(normalizeLocale('JA_jp'), 'ja');
   // Explicit script tags take precedence over regional defaults.
   assert.equal(normalizeLocale('zh'), 'zh-CN');
   assert.equal(normalizeLocale('zh-CN'), 'zh-CN');
@@ -164,7 +168,13 @@ test('Intl formatters follow the active locale', () => {
   assert.equal(formatNumber(1234.5), '1,234.5');
   setLocale('ru');
   assert.equal(formatDate(date, options), '15 января 2026 г.');
+  assert.equal(formatRelativeTime(-5, 'minute'), '5 минут назад');
   assert.equal(formatNumber(1234.5), '1 234,5');
+  // Japanese keeps a number and its unit together, as the catalog does.
+  setLocale('ja');
+  assert.equal(formatDate(date, options), '2026年1月15日');
+  assert.equal(formatRelativeTime(-5, 'minute'), '5分前');
+  assert.equal(formatRelativeTime(-3, 'day'), '3日前');
 });
 
 function fakeElement({ text = '', attributes = {} } = {}) {

src/i18n/index.js

@@ -17,11 +17,18 @@ import {
   writeStoredLocale,
 } from './locale.js';
 import es from './locales/es.json' with { type: 'json' };
+import ja from './locales/ja.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({
+  es,
+  ja,
+  ru,
+  'zh-CN': zhCN,
+  'zh-Hant': zhHant,
+});
 
 let currentLocale = DEFAULT_LOCALE;
 
@@ -201,13 +208,19 @@ export function formatUtcDayMonth(value) {
 
 /**
  * Locale-aware relative time (Intl.RelativeTimeFormat), e.g.
- * formatRelativeTime(-5, 'minute') → '5 minutes ago' / '5 минут назад'.
+ * formatRelativeTime(-5, 'minute') → '5 minutes ago' / '5 минут назад' /
+ * '5分前'.
  */
 export function formatRelativeTime(value, unit = 'second', options) {
-  return cachedFormatter('relative', Intl.RelativeTimeFormat, {
+  const text = cachedFormatter('relative', Intl.RelativeTimeFormat, {
     numeric: 'auto',
     ...options,
   }).format(value, unit);
+  // CLDR spaces Japanese (5 分前); the ja catalog writes the number and its
+  // unit together (5分前), so the two must not differ on one screen.
+  return currentLocale === 'ja'
+    ? text.replace(/(?<=\d) (?=\p{Script=Han})/gu, '')
+    : text;
 }
 
 /** Collapse markup whitespace so a message reads the same in HTML and JS. */

src/i18n/locale.js

@@ -8,12 +8,20 @@ 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',
+  'es',
+  'ja',
+  'ru',
+  'zh-CN',
+  'zh-Hant',
+]);
 
 /** Each locale named in its own language, for the selector. */
 export const LOCALE_NAMES = Object.freeze({
   en: 'English',
   es: 'Español',
+  ja: '日本語',
   ru: 'Русский',
   'zh-CN': '中文（简体）',
   'zh-Hant': '中文（繁體）',
@@ -23,7 +31,7 @@ export const LOCALE_NAMES = Object.freeze({
 const RTL_LOCALES = Object.freeze([]);
 
 /**
- * Map any language tag to a shipped locale: 'ru-RU' and 'RU' → 'ru',
+ * Map any language tag to a shipped locale: 'ru-RU' and 'RU' → 'ru', 'ja-JP' → 'ja',
  * 'zh', 'zh-CN' and 'zh-Hans-SG' → 'zh-CN';
  * 'zh-Hant', 'zh-TW', 'zh-HK' and 'zh-MO' → 'zh-Hant'.
  * @returns {string|null}

src/layers/directions/index.js

@@ -20,7 +20,11 @@ import * as Cesium from 'cesium';
 import { roadLabel } from '../../data/routeSteps.js';
 import { t, msg, formatNumber, translateKnown } from '../../i18n/index.js';
 import { pointerOwnerName } from '../../data/pointerOwnerNames.js';
-import { formatQuantity } from '../../ui/unitLabels.js';
+import {
+  formatQuantity,
+  quantitySeparator,
+  unitLabel,
+} from '../../ui/unitLabels.js';
 
 export const DIRECTIONS_STEP_OVERLAY_SOURCE_ID = 'directions-step';
 export const DIRECTIONS_STEP_OVERLAY_SOURCE_OPTIONS = Object.freeze({
@@ -137,7 +141,9 @@ export function routeDurationText(seconds) {
   if (minutes < 60) return formatQuantity(minutes, 'min');
   const hours = formatQuantity(Math.floor(minutes / 60), 'h');
   const rest = minutes % 60;
-  return rest ? `${hours}\u00a0${formatQuantity(rest, 'min')}` : hours;
+  if (!rest) return hours;
+  // "1 h 5 min"; Japanese runs the parts together: 1時間5分.
+  return `${hours}${quantitySeparator(unitLabel('h'))}${formatQuantity(rest, 'min')}`;
 }
 
 /** "left", "slightly right", … as it reads inside a maneuver sentence. */

src/ui/localePicker.test.mjs

@@ -40,7 +40,7 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['ru', 'en', 'es', 'zh-CN', 'zh-Hant'],
+    ['ru', 'en', 'es', 'zh-CN', 'zh-Hant', 'ja'],
   );
   assert.deepEqual(
     codes(
@@ -50,7 +50,7 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['es', 'en', 'ru', 'zh-CN', 'zh-Hant'],
+    ['es', 'en', 'ru', 'zh-CN', 'zh-Hant', 'ja'],
   );
   assert.deepEqual(
     codes(
@@ -60,7 +60,7 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['en', 'es', 'ru', 'zh-CN', 'zh-Hant'],
+    ['en', 'es', 'ru', 'zh-CN', 'zh-Hant', 'ja'],
   );
   const rows = buildLocaleOptions({
     locales: MANY,
@@ -263,7 +263,7 @@ test('keyboard model: open on the current language, move, choose, close', () =>
   assert.deepEqual(model.keydown({ key: 'ArrowDown' }), { handled: true });
   assert.equal(model.activeOption.code, 'en');
   model.keydown({ key: 'End' });
-  assert.equal(model.activeOption.code, 'zh-Hant');
+  assert.equal(model.activeOption.code, 'ja');
   model.keydown({ key: 'Home' });
   assert.equal(model.activeOption.code, 'ru');
   model.keydown({ key: 'ArrowUp' });

src/ui/unitLabels.js

@@ -1,4 +1,4 @@
-import { formatNumber, msg, t } from '../i18n/index.js';
+import { formatNumber, getLocale, msg, t } from '../i18n/index.js';
 
 // Unit ids stay English in data, params and AI-tool readings; only the label
 // shown on the page is translated. dBZ and °C read the same in every language.
@@ -23,6 +23,17 @@ export function unitLabel(unit) {
   return Object.hasOwn(UNIT_LABELS, unit) ? t(UNIT_LABELS[unit]) : unit || '';
 }
 
+/**
+ * What goes between a number and its unit label: a no-break space, except
+ * before a Japanese unit word, which follows the number directly (5分, 1時間).
+ */
+export function quantitySeparator(label) {
+  return getLocale() === 'ja' &&
+    /^[\p{Script=Han}\p{Script=Hiragana}\p{Script=Katakana}]/u.test(label)
+    ? ''
+    : '\u00a0';
+}
+
 /**
  * A number and its unit that never break apart: "22,0 км/ч". Readings carry
  * no digit grouping ("1008 hPa"), as on weather charts.
@@ -30,7 +41,7 @@ export function unitLabel(unit) {
 export function formatQuantity(value, unit, options) {
   const label = unitLabel(unit);
   const number = formatNumber(value, { useGrouping: false, ...options });
-  return label ? `${number}\u00a0${label}` : number;
+  return label ? `${number}${quantitySeparator(label)}${label}` : number;
 }
 
 /**

src/ui/unitLabels.test.mjs

@@ -44,3 +44,14 @@ test('other languages get their decimal separator and no digit grouping', () =>
     setLocale('en');
   }
 });
+
+test('Japanese unit words follow the number directly; symbols keep the space', () => {
+  try {
+    setLocale('ja');
+    assert.equal(formatQuantity(5, 'min'), '5分');
+    assert.equal(formatQuantity(1, 'h'), '1時間');
+    assert.equal(formatQuantity(95, 'kt'), '95\u00a0kt');
+  } finally {
+    setLocale('en');
+  }
+});