Merge pull request #1478 from bilawalsidhu/german/hal-642-ja

Japanese in the language picker: the full catalog, counters, unit words joined to their numbers (5分前, 1時間5分), lower-case HUD units as in Chinese, and the CJK label rules plus strict line breaking for Japanese. Based on translations by @abiyeenzo (#913). Co-authored-by: Enzo Abyie <[email protected]>
2026-11-04 10:24:02 +00:00 · 2026-10-29 19:58:17 +04:00
commit bcabdff88d
@@ -0,0 +1,4 @@
+- Add Japanese (ja) to the language picker, with year-first dates, Japanese
+  counters, unit words joined to their numbers (5分前, 1時間5分) and CJK label
+  rules for Japanese text. Based on translations by @abiyeenzo (#913)
+  (German, @gekh, #1478).
@@ -3784,7 +3784,7 @@ test:track` 43 tracking invariants · headless QA harnesses under

 ### Interface localization (October 2026)

-Shipped locales: **en** (source and fallback), **de**, **es**, **fr**, **it**, **pt** (Brazilian Portuguese), **ru**, **uk**, **zh-CN** and **zh-Hant**. The code lives in
+Shipped locales: **en** (source and fallback), **de**, **es**, **fr**, **it**, **ja**, **pt** (Brazilian Portuguese), **ru**, **uk**, **zh-CN** and **zh-Hant**. The code lives in
 `src/i18n/`. How to mark UI text: [`docs/I18N.md`](./I18N.md); translator workflow:
 [`docs/TRANSLATORS.md`](./TRANSLATORS.md).

@@ -1,6 +1,6 @@
 # Translating God's Eye View

-Shipped languages: **English** (source and fallback), **German** (`de`), **Spanish** (`es`), **French** (`fr`), **Italian** (`it`), **Brazilian Portuguese** (`pt`), **Russian** (`ru`), **Ukrainian** (`uk`), **Simplified Chinese** (`zh-CN`) and **Traditional Chinese** (`zh-Hant`).
+Shipped languages: **English** (source and fallback), **German** (`de`), **Spanish** (`es`), **French** (`fr`), **Italian** (`it`), **Japanese** (`ja`), **Brazilian Portuguese** (`pt`), **Russian** (`ru`), **Ukrainian** (`uk`), **Simplified Chinese** (`zh-CN`) and **Traditional Chinese** (`zh-Hant`).

 ## How it works

@@ -63,4 +63,4 @@ These are contracts, not copy: layer ids and registry keys, status enums and oth

 ## Language notes

-Each language keeps its glossary, plural forms, units and style in its own file, `docs/translations/<code>.md`: [German](./translations/de.md), [Spanish](./translations/es.md), [French](./translations/fr.md), [Italian](./translations/it.md), [Brazilian Portuguese](./translations/pt.md), [Russian](./translations/ru.md), [Ukrainian](./translations/uk.md), [Simplified Chinese](./translations/zh-CN.md), [Traditional Chinese](./translations/zh-Hant.md). Read it before translating, and add a term there when you settle on one.
+Each language keeps its glossary, plural forms, units and style in its own file, `docs/translations/<code>.md`: [German](./translations/de.md), [Spanish](./translations/es.md), [French](./translations/fr.md), [Italian](./translations/it.md), [Japanese](./translations/ja.md), [Brazilian Portuguese](./translations/pt.md), [Russian](./translations/ru.md), [Ukrainian](./translations/uk.md), [Simplified Chinese](./translations/zh-CN.md), [Traditional Chinese](./translations/zh-Hant.md). Read it before translating, and add a term there when you settle on one.
@@ -0,0 +1,112 @@
+# Japanese (`ja`)
+
+Catalog: `src/i18n/locales/ja.json`. General rules: [TRANSLATORS.md](../TRANSLATORS.md).
+
+Translation source: abiyeenzo (#913).
+
+## Style
+
+- Sentences use です／ます: 「キーを保存しました」, 「もう一度お試しください」. Labels, buttons and HUD chips are short nouns or verb stems without a final 。: 「再試行」, 「保存」, 「ライブ」, 「オフ」.
+- Japanese has no case: an UPPERCASE English label becomes the same short Japanese label. Codes, units and names stay in their own case (HDG, ADS-B, km).
+- Full-width punctuation in Japanese text: 、。：？！（）「」. Quote names and titles with 「」: 「{shot}」を削除しますか？ Keep `·` as the HUD separator, `…` for an ellipsis and `—`, `→`, `↗` as in English. A dash inside a sentence becomes 。 or ：.
+- Button names cited in running text go in ［］: ［次へ］を使ってください.
+- No space between Japanese and Latin letters, digits or a `{placeholder}`: 「AIS船舶」, 「Spaceを長押しで話す」, 「{count}件」, 「{name}を表示」.
+- Two exceptions keep the space: a Japanese label before its value in a readout (「雲量 {pct}%」, 「ステーション {id}」, 「高度 {altitude}」), and the state words in toggles (「CCTV オン」, 「ラジオ オフ」).
+- Waiting states are 「X待ち」, not 「Xを待機中」: 「観測データ待ち」, 「進路/予報円は第{number}報待ち」, 「RTL-SDRデバイスの接続待ち…」. 待機中 is for something on standby with no object: 「フィード待機中」, 「音声待機中」.
+- Key names keep their own case in running text and hints: Tab, Enter, Space, Esc (「Tabでプレビュー · Enter / Spaceで選択」). Text that CSS upper-cases shows them in capitals, as in English.
+- Loanwords are katakana with the long-vowel mark, as in Microsoft and Apple style: ユーザー, ブラウザー, ビューアー, プロバイダー, レイヤー, フィルター, モニター, パラメーター. Pick one katakana form per term and keep it (see the glossary).
+- Product, provider and dataset names stay in Latin script: Google Maps, Cesium ion, OpenSky, CelesTrak, NASA FIRMS, Sentinel-2, KartaView. Google's own product names use Google's Japanese, joined like any Latin word: Googleストリートビュー. Nepal place names in the Bhote Koshi scenes stay in Latin script, as in zh-CN; country and well-known city names are translated (ネパール, 東京, オースティン).
+
+## Numbers, units and dates
+
+- Units: km, m, km/h, m/s, kt, ft, mph, hPa, MW, dB, °, % stay as written, with the English spacing (「250 km」, 「{frp} MW」, 「95 kt」). Code-built cockpit distances follow this too (`cockpitUnitCase` skips the HUD upper-casing for ja, as for zh). The cockpit's own speed caption is the HUD code KT, in 対地速度 · KT and under the readout.
+- Number ranges keep the English en dash, not ～: 「2–6日ごと」, 「50–99%」, 「南緯25°–北緯80°」.
+- Time units are words written straight after the number: 秒, 分, 時間, 日 (「5分前」, 「{count}時間」, 「1時間5分」). `formatQuantity` and `formatRelativeTime` drop the space for Japanese unit words, so code-built values match the catalog.
+- Counters follow the thing counted: 機 (aircraft), 隻 (ships), 基 (satellites), 台 (cameras, vehicles), 局 (stations), 件 (records, results, events), か所 (sites), 個 (generic). Prefer a counter to a bare number.
+- Dates come from `Intl` and read year first: 2026年8月26日. Coordinates in prose are 北緯 / 東経; HUD hemisphere letters stay N, S, E, W.
+
+## Plurals
+
+`Intl.PluralRules('ja')` has one category, `other`: a `tn()` entry has only that form. Put the counter next to the number: 「航空機{n}機」, 「船舶{n}隻」, 「メッセージ {count}件」.
+
+## Glossary
+
+| English                                   | 日本語                                  |
+| ----------------------------------------- | --------------------------------------- |
+| layer / data layer                        | レイヤー / データレイヤー               |
+| feed                                      | フィード                                |
+| source / data source / attribution        | ソース / データソース / 出典            |
+| LIVE (status) / live data                 | ライブ / ライブデータ                   |
+| SIMULATED                                 | シミュレーション                        |
+| stale / degraded / unavailable            | 更新遅延 / 性能低下 / 利用不可          |
+| cached (status)                           | キャッシュの（キャッシュの予報）        |
+| PARTIAL (feed state)                      | 部分的                                  |
+| upstream (remote data source)             | 配信元                                  |
+| retry                                     | 再試行                                  |
+| key (API key) / POWER UP                  | キー（APIキー）/ パワーアップ           |
+| Provider Settings                         | プロバイダー設定                        |
+| globe / map / map source / basemap        | 地球儀 / 地図 / マップソース / ベースマップ |
+| mapped (OSM-mapped sites)                 | マップ済み                              |
+| aircraft / flight / military flights      | 航空機 / フライト / 軍用機              |
+| FLIGHT {count} (a rocket stage's nth flight) | {count}回目の飛行                    |
+| vessel, ship                              | 船舶                                    |
+| satellite                                 | 衛星                                    |
+| launch (rocket) / space mission           | 打ち上げ / 宇宙ミッション               |
+| stage (rocket) / downrange                | 段 / ダウンレンジ                       |
+| contact (tracked object)                  | コンタクト                              |
+| installation, site                        | 施設                                    |
+| camera / CCTV camera                      | カメラ / CCTVカメラ                     |
+| earthquake / active fire / fire perimeter | 地震 / 火災検知 / 延焼範囲              |
+| contained / containment (fire)            | 封じ込め / 封じ込め率                   |
+| scene / shot                              | シーン / ショット                       |
+| briefing / panel / dock                   | ブリーフィング / パネル / ドック        |
+| preset / visual preset                    | プリセット / ビジュアルプリセット       |
+| Tactical / Operator / Minimal / Cyber     | タクティカル / オペレーター / ミニマル / サイバー |
+| Scope (circular viewport mask) / keyhole  | スコープ / キーホール                   |
+| Clean UI                                  | クリーンUI                              |
+| cockpit                                   | コックピット                            |
+| heading / altitude / ground speed         | 機首方位 / 高度 / 対地速度              |
+| track (TRK, direction over the ground)    | 対地針路                                |
+| HDG / BRG / CRS / FOV / SPD / POS        | そのまま（HUDコード）                   |
+| squawk                                    | スコーク                                |
+| radio failure / emergency (7600 / 7700)   | 通信機故障 / 緊急事態                   |
+| map heading / North up                    | 方位 / 北を上に                         |
+| Street Level / Street View (Google)       | ストリートレベル / ストリートビュー     |
+| Recent Imagery                            | 最近の衛星画像                          |
+| Global Context / Context (panel)          | グローバルコンテキスト / コンテキスト   |
+| radio (station) / tune / seek             | ラジオ（局）/ 選局・同調 / シーク       |
+| Public Safety / SAFETY (radio category)   | 警察・消防                              |
+| transit / bikeshare                       | 公共交通 / シェアサイクル               |
+| occupancy: empty / standing room only / crushed | 乗客なし / 立ち乗りのみ / 非常に混雑 |
+| traffic flow (TomTom)                     | 交通流                                  |
+| Previous / Next                           | 前へ / 次へ                             |
+| SIG / NEWS / LOCAL (briefing tabs)        | シグナル / ニュース / ローカル          |
+| compass points (N, NNE, NE, ENE, …)       | 北, 北北東, 北東, 東北東, …             |
+| weather field / FIELD (selector)          | 要素                                    |
+| weather model / forecast lead hours       | モデル / 予報時間                       |
+| valid (forecast time) / issued            | 対象時刻 / 発表                         |
+| radar reflectivity / lightning density    | レーダー反射強度 / 雷密度               |
+| cyclone, storm (NHC/CPHC) / advisory      | サイクロン / 情報（第N報）; alone: サイクロン情報 |
+| potential tropical cyclone (NHC PC)       | サイクロン化のおそれがある擾乱          |
+| forecast uncertainty cone                 | 予報円                                  |
+| tropical storm / tropical depression      | 熱帯暴風雨 / 熱帯低気圧                 |
+| scene cloud / mosaic / daily overview     | シーン雲量 / モザイク / 日次概観        |
+| box (Recent Imagery area)                 | 範囲                                    |
+| WINDOW (search radius around a subject)   | 範囲                                    |
+| coverage / coverage % / full, partial     | カバー範囲 / カバー率（%のみ）/ 全体, 一部 |
+| pin (Recent Imagery)                      | 固定                                    |
+| clear day (Recent Imagery)                | 雲の少ない日                            |
+| outline / mark (map annotation)           | 輪郭 / マーク                           |
+| share (a view or link)                    | 共有                                    |
+| import / export (project, presets)        | インポート / エクスポート               |
+| EXPORT (image, PNG)                       | 書き出し                                |
+| voice (the voice assistant)               | 音声アシスタント / 音声機能             |
+| activate (a control, screen-reader text)  | 押す（「押すと…」）                      |
+| AI agent                                  | AIエージェント                          |
+| frame (bring into view)                   | 視野に収める                            |
+| story beat / evidence beat                | ストーリー区切り / 証拠の区切り         |
+| camera pose / camera move                 | カメラの姿勢 / 移動                     |
+| roundabout / ramp / exit                  | ロータリー / ランプ / 出口              |
+| reduced motion                            | 動きを減らす                            |
+| NOT AN ALL-CLEAR                          | 安全の保証ではありません                |
+| … Watch (scene titles: Earth, Orbital)    | 監視（地球監視, 軌道監視）              |
@@ -443,6 +443,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -487,6 +488,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -522,6 +524,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -549,6 +552,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -571,6 +575,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -596,6 +601,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -628,6 +634,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -668,6 +675,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -690,6 +698,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -853,6 +862,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -981,6 +991,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1055,6 +1066,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1109,6 +1121,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1177,6 +1190,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1212,6 +1226,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1248,6 +1263,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1284,6 +1300,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1323,6 +1340,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1371,6 +1389,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1413,6 +1432,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1469,6 +1489,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1504,6 +1525,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1558,6 +1580,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1627,6 +1650,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1662,6 +1686,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1708,6 +1733,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1736,6 +1762,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1798,6 +1825,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -1866,6 +1894,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -2754,6 +2783,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3345,6 +3375,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3461,6 +3492,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3490,6 +3522,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3531,6 +3564,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3564,6 +3598,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3661,6 +3696,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3722,6 +3758,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -3982,6 +4019,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -4031,6 +4069,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -4090,6 +4129,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -4112,6 +4152,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -4177,6 +4218,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -4381,6 +4423,7 @@
      "src/i18n/locales/es.json",
      "src/i18n/locales/fr.json",
      "src/i18n/locales/it.json",
+      "src/i18n/locales/ja.json",
      "src/i18n/locales/pt.json",
      "src/i18n/locales/ru.json",
      "src/i18n/locales/uk.json",
@@ -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',
@@ -8,7 +8,10 @@ import { formatNumber, getLocale, t } from './i18n/index.js';
 import { unitLabel } from './ui/unitLabels.js';
 import { localizePlaceName } from './ui/placeNames.js';

-/** An upper-case HUD quantity such as `13KM` / `13КМ`, in the active language. */
+/**
+ * An upper-case HUD quantity such as `13KM` / `13КМ`, in the active language.
+ * Chinese and Japanese have no case and keep the catalog's `13 km`.
+ */
 export function hudQuantity(value, unit, digits = 0) {
  const number = formatNumber(value, {
    useGrouping: false,
@@ -16,7 +19,7 @@ export function hudQuantity(value, unit, digits = 0) {
    maximumFractionDigits: digits,
  });
  const label = unitLabel(unit);
-  if (getLocale().startsWith('zh-'))
+  if (/^(zh|ja)(-|$)/.test(getLocale()))
    return label ? `${number} ${label}` : number;
  return `${number}${label.toUpperCase()}`;
 }
@@ -5,6 +5,7 @@ import {
  applyDocumentTranslations,
  formatDate,
  formatNumber,
+  formatRelativeTime,
  msg,
  persistLocaleAndReload,
  setLocale,
@@ -47,6 +48,9 @@ test('normalizeLocale folds regional variants and rejects unshipped tags', () =>
  assert.equal(normalizeLocale('xx'), null);
  assert.equal(normalizeLocale('it-IT'), 'it');
  assert.equal(normalizeLocale('it_CH'), 'it');
+  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');
@@ -214,7 +218,13 @@ 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 = {} } = {}) {
@@ -20,6 +20,7 @@ import de from './locales/de.json' with { type: 'json' };
 import es from './locales/es.json' with { type: 'json' };
 import fr from './locales/fr.json' with { type: 'json' };
 import it from './locales/it.json' with { type: 'json' };
+import ja from './locales/ja.json' with { type: 'json' };
 import pt from './locales/pt.json' with { type: 'json' };
 import ru from './locales/ru.json' with { type: 'json' };
 import uk from './locales/uk.json' with { type: 'json' };
@@ -31,6 +32,7 @@ const CATALOGS = Object.freeze({
  es,
  fr,
  it,
+  ja,
  pt,
  ru,
  uk,
@@ -216,13 +218,19 @@ 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. */
@@ -0,0 +1,21 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { setLocale } from './index.js';
+import {
+  cockpitUnitCase,
+  formatCockpitDistance,
+} from '../ui/cockpitPresentation.js';
+
+test('Japanese cockpit distances keep the unit in its own case', () => {
+  try {
+    setLocale('ja');
+    assert.equal(formatCockpitDistance(14000), '14 km');
+    assert.equal(formatCockpitDistance(9500), '9.5 km');
+    assert.equal(cockpitUnitCase('km'), 'km');
+    setLocale('en');
+    assert.equal(formatCockpitDistance(14000), '14 KM');
+    assert.equal(cockpitUnitCase('km'), 'KM');
+  } finally {
+    setLocale('en');
+  }
+});
@@ -0,0 +1,22 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { setLocale } from './index.js';
+import { hudQuantity, LOCALIZED_LOCALITY } from '../hudLocalityFormat.js';
+import { formatCockpitDistance } from '../ui/cockpitPresentation.js';
+
+// revmain-opus-ja-i1-1: ja has no case, so HUD units keep the catalog case
+// (km), as the cockpit already does and docs/translations/ja.md requires.
+test('Japanese HUD units keep their case, like the cockpit', () => {
+  try {
+    setLocale('ja');
+    assert.equal(formatCockpitDistance(14000), '14 km');
+    assert.equal(hudQuantity(13, 'km'), '13 km');
+    assert.equal(hudQuantity(1.5, 'km', 1), '1.5 km');
+    assert.equal(
+      LOCALIZED_LOCALITY.near({ poi: 'Shibuya', city: 'Tokyo', distKm: 13 }),
+      'SHIBUYA（東京）付近 13 km',
+    );
+  } finally {
+    setLocale('en');
+  }
+});
@@ -14,6 +14,7 @@ export const LOCALES = Object.freeze([
  'es',
  'fr',
  'it',
+  'ja',
  'pt',
  'ru',
  'uk',
@@ -28,6 +29,7 @@ export const LOCALE_NAMES = Object.freeze({
  es: 'Español',
  fr: 'Français',
  it: 'Italiano',
+  ja: '日本語',
  pt: 'Português (Brasil)',
  ru: 'Русский',
  uk: 'Українська',
@@ -40,7 +42,7 @@ const RTL_LOCALES = Object.freeze([]);

 /**
 * Map any language tag to a shipped locale: 'ru-RU' and 'RU' → 'ru',
-  'de',
+ * 'de-AT' and 'de_CH' → 'de', 'ja-JP' → 'ja',
 * 'pt-BR' and 'pt-PT' → 'pt' (Brazilian Portuguese),
 * 'zh', 'zh-CN' and 'zh-Hans-SG' → 'zh-CN';
 * 'zh-Hant', 'zh-TW', 'zh-HK' and 'zh-MO' → 'zh-Hant'.
@@ -638,6 +638,55 @@
    "ΔN",
    "▲ {frp} MW"
  ],
+  "ja": [
+    "1090 MHz",
+    "978 MHz UAT",
+    "AIS: --",
+    "AIS: {name}",
+    "BRG {value}°",
+    "BRG —",
+    "CAL {value}",
+    "CAL · {badge}",
+    "CCTV",
+    "CH {index} / {total}",
+    "CRS {value}°",
+    "CRT",
+    "FLIR",
+    "FLT",
+    "FM MHZ",
+    "FOV",
+    "FOV {value}°",
+    "FT",
+    "GEO",
+    "HDG",
+    "HDG {value}°",
+    "Ironbow",
+    "Landsat 8/9",
+    "MSG/S",
+    "NVG",
+    "POS: {time}Z",
+    "REC",
+    "S2 GhostMaps",
+    "SRC {value}",
+    "Sentinel-2",
+    "USB {rate} msg/s",
+    "WHOT/BHOT",
+    "dB",
+    "ft",
+    "hPa",
+    "km",
+    "km/h",
+    "kt",
+    "mph",
+    "{city} CCTV",
+    "{rate} msg/s",
+    "{source} HTTP {status}",
+    "{speed} kn",
+    "{type}  SPD: {speed}  HDG: {heading}",
+    "ΔE",
+    "ΔN",
+    "▲ {frp} MW"
+  ],
  "pt": [
    "1090 MHz",
    "978 MHz UAT",
@@ -17,6 +17,9 @@ test('Chinese HUD and cockpit units keep their case without spacing coordinates'
    assert.equal(formatCockpitDistance(14000), '14\u00a0km');
    assert.equal(LOCALIZED_LOCALITY.sector({ latDeg: 21.33, lonDeg: -77.5 }),
      '扇区 21.33N 77.50W');
+    setLocale('ja');
+    assert.equal(hudQuantity(13, 'km'), '13 km');
+    assert.equal(hudQuantity(1.5, 'km', 1), '1.5 km');
    setLocale('en');
    assert.equal(hudQuantity(0, 'km'), '0KM');
    assert.equal(hudQuantity(2069, 'km', 1), '2069.0KM');
@@ -26,7 +26,11 @@ import {
  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({
@@ -131,7 +135,9 @@ 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. */
@@ -1,6 +1,6 @@
 /** Contact readouts and nearby-signal presentation for the Cockpit controller. */
 import * as Cesium from 'cesium';
-import { formatNumber, getLocale, t, tn } from '../i18n/index.js';
+import { formatNumber, t, tn } from '../i18n/index.js';
 import { unitLabel } from './unitLabels.js';
 import {
  bearingBetweenCoordinates,
@@ -8,14 +8,17 @@ import {
  relativeBearing,
  resolveCockpitContextReadout,
 } from '../cockpitMath.js';
-import { formatCockpitDistance } from './cockpitPresentation.js';
+import {
+  cockpitUnitCase,
+  formatCockpitDistance,
+} from './cockpitPresentation.js';

 /** The Context scope line in the active language (see cockpitMath.js). */
 const LOCALIZED_CONTEXT_SCOPE = Object.freeze({
  window: ({ label, radiusKm }) =>
    t('{label} · {radius} AIR/SEA WINDOW', {
      label,
-      radius: `${radiusKm === null ? '—' : formatNumber(radiusKm)}\u00a0${getLocale().startsWith('zh-') ? unitLabel('km') : unitLabel('km').toUpperCase()}`,
+      radius: `${radiusKm === null ? '—' : formatNumber(radiusKm)}\u00a0${cockpitUnitCase(unitLabel('km'))}`,
    }),
  installations: ({ scope, coverage }) =>
    t('{scope} · INSTALLATIONS {coverage}', { scope, coverage }),
@@ -149,7 +149,15 @@ export function formatCockpitDistance(distanceM) {
    minimumFractionDigits: digits,
    maximumFractionDigits: digits,
  });
-  return getLocale().startsWith('zh-') ? distance : distance.toUpperCase();
+  return cockpitUnitCase(distance);
+}
+
+/**
+ * Upper-case a cockpit unit the HUD way (`9.5 KM`), except in Chinese and
+ * Japanese, which have no case and keep units as the catalog writes them.
+ */
+export function cockpitUnitCase(text) {
+  return /^(zh|ja)(-|$)/.test(getLocale()) ? text : text.toUpperCase();
 }

 export function formatCockpitWindDirection(value) {
@@ -43,7 +43,7 @@ test('the current language comes first, the rest by their own names', () => {
        nativeNames: LOCALE_NAMES,
      }),
    ),
-    ['ru', 'uk', 'de', 'en', 'es', 'fr', 'it', 'pt', 'zh-CN', 'zh-Hant'],
+    ['ru', 'uk', 'de', 'en', 'es', 'fr', 'it', 'pt', 'zh-CN', 'zh-Hant', 'ja'],
  );
  assert.deepEqual(
    codes(
@@ -53,7 +53,7 @@ test('the current language comes first, the rest by their own names', () => {
        nativeNames: LOCALE_NAMES,
      }),
    ),
-    ['es', 'de', 'en', 'fr', 'it', 'pt', 'ru', 'uk', 'zh-CN', 'zh-Hant'],
+    ['es', 'de', 'en', 'fr', 'it', 'pt', 'ru', 'uk', 'zh-CN', 'zh-Hant', 'ja'],
  );
  assert.deepEqual(
    codes(
@@ -63,7 +63,7 @@ test('the current language comes first, the rest by their own names', () => {
        nativeNames: LOCALE_NAMES,
      }),
    ),
-    ['en', 'de', 'es', 'fr', 'it', 'pt', 'ru', 'uk', 'zh-CN', 'zh-Hant'],
+    ['en', 'de', 'es', 'fr', 'it', 'pt', 'ru', 'uk', 'zh-CN', 'zh-Hant', 'ja'],
  );
  const rows = buildLocaleOptions({
    locales: MANY,
@@ -1,6 +1,7 @@
-/* Tight tracking keeps Chinese labels readable; preserve Latin tracking for
-   intel HUD readouts and content marked translate="no", including its containers. */
-html:lang(zh)
+/* Chinese and Japanese text. Tight tracking keeps CJK labels readable;
+   preserve Latin tracking for intel HUD readouts and content marked
+   translate="no", including its containers. */
+html:is(:lang(zh), :lang(ja))
  body
  :not(
    #intel-hud,
@@ -12,40 +13,67 @@ html:lang(zh)
  letter-spacing: 0.02em !important;
 }

-/* Keep small Chinese labels legible at a minimum of 9px. */
-html:lang(zh) #command-dock .gev-mic-label,
-html:lang(zh) #command-dock #gev-voice-detail,
-html:lang(zh) .gev-voice-tier-btn,
-html:lang(zh) .panel-layer-toggle {
+/* Japanese line breaking: never start a line with ー, a small kana or closing
+   punctuation (プレビュ / ー). */
+html:lang(ja) body {
+  line-break: strict;
+}
+
+/* Keep small CJK labels legible at a minimum of 9px. */
+html:is(:lang(zh), :lang(ja)) #command-dock .gev-mic-label,
+html:is(:lang(zh), :lang(ja)) #command-dock #gev-voice-detail,
+html:is(:lang(zh), :lang(ja)) .gev-voice-tier-btn,
+html:is(:lang(zh), :lang(ja)) .panel-layer-toggle {
  font-size: 9px;
 }

 /* A two-glyph button label must not break between its glyphs. */
-html:lang(zh) .pp-mode-btn {
+html:is(:lang(zh), :lang(ja)) .pp-mode-btn {
+  white-space: nowrap;
+}
+
+/* Japanese segment labels are short words (すべて, 平面): keep each whole. */
+html:lang(ja) .gev-segment {
  white-space: nowrap;
 }

 /* Keep unit symbols in their catalog case, including the cockpit readouts. */
-html:lang(zh) #intel-hud *,
-html:lang(zh) #cockpit-hud * {
+html:is(:lang(zh), :lang(ja)) #intel-hud *,
+html:is(:lang(zh), :lang(ja)) #cockpit-hud * {
  text-transform: none;
 }

-/* Move short travel modes (步行 / 骑行) to the next line as whole words. */
-html:lang(zh) [data-layer-id='directions'] .data-toggle-meta {
+/* Move short travel modes (步行 / 骑行, 徒歩 / 自転車) to the next line as
+   whole words. */
+html:is(:lang(zh), :lang(ja)) [data-layer-id='directions'] .data-toggle-meta {
  word-break: keep-all;
  overflow-wrap: break-word;
 }

 /* Leave room for the complete sensor name and resolution on two lines. */
-html:lang(zh) .recent-imagery-readout .ri-strip {
+html:is(:lang(zh), :lang(ja)) .recent-imagery-readout .ri-strip {
  height: 131px;
 }
-html:lang(zh) .recent-imagery-readout .ri-card {
+html:is(:lang(zh), :lang(ja)) .recent-imagery-readout .ri-card {
  height: 123px;
  grid-template-rows: 42px 13px 22px 11px 18px;
 }
-html:lang(zh) .recent-imagery-readout .ri-card-sensor {
+html:is(:lang(zh), :lang(ja)) .recent-imagery-readout .ri-card-sensor {
  white-space: normal;
  text-overflow: clip;
 }
+
+/* The Japanese imagery slot line wraps at its · separators, never inside a
+   word (プレ / ビュー); a run too long for the line still breaks. */
+html:lang(ja) .recent-imagery-readout .ri-slot-value {
+  word-break: keep-all;
+  overflow-wrap: break-word;
+}
+
+/* Japanese layer status lines wrap at their spaces and · separators, so an
+   age such as 1分以内 stays whole (更新 1 / 分以内); a run too long for the
+   line still breaks. */
+html:lang(ja) .data-toggle-meta {
+  word-break: keep-all;
+  overflow-wrap: break-word;
+}
@@ -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;
 }

 /**
@@ -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');
+  }
+});