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/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. */