i18n: add Traditional Chinese (zh-TW)

Add a complete Taiwan Traditional Chinese catalog, locale selection,
Chinese readout formatting, translation notes and regression coverage.
Seed translations from #724 and #652 and adapt the zh-CN catalog.

Co-authored-by: caxer <[email protected]>
Co-authored-by: tbdavid2019 <[email protected]>
Co-authored-by: Enzo Abyie <[email protected]>
Co-authored-by: EDIT-Aeterna <[email protected]>

docs/CURRENT-STATE.md

@@ -3583,7 +3583,7 @@ test:track` 43 tracking invariants · headless QA harnesses under
 
 ### Interface localization (October 2026)
 
-Shipped locales: **en** (source and fallback), **es**, **ru** and **zh-CN**. The code lives in
+Shipped locales: **en** (source and fallback), **es**, **ru**, **zh-CN** and **zh-TW**. The code lives in
 `src/i18n/`. How to mark UI text: [`docs/I18N.md`](./I18N.md); translator workflow:
 [`docs/TRANSLATORS.md`](./TRANSLATORS.md).
 
@@ -3594,8 +3594,8 @@ Shipped locales: **en** (source and fallback), **es**, **ru** and **zh-CN**. The
   value). English has no catalog; every other locale is
   `src/i18n/locales/<code>.json`, and a missing entry falls back to English.
 - **Locale choice.** `?lang=` → stored choice (`gev:locale:v1`) →
-  `navigator.languages` → English. Chinese tags map to `zh-CN`; tags containing
-  `Hant`, `TW`, `HK` or `MO` are skipped. `?lang=` is not stored, and share links drop
+  `navigator.languages` → English. Chinese tags default to `zh-CN`; `Hant`, `TW`, `HK` and `MO`
+  select `zh-TW`. Explicit `Hans` selects `zh-CN` regardless of region. `?lang=` is not stored, and share links drop
   it, so a recipient keeps their own language. The globe picker in the
   bottom-right corner (`src/ui/localePicker.js`) stores the choice, drops
   `?lang=` (keeps it only when storage is blocked) and reloads. It asks first

docs/TRANSLATORS.md

@@ -1,6 +1,6 @@
 # Translating God's Eye View
 
-Shipped languages: **English** (source and fallback), **Spanish** (`es`), **Russian** (`ru`) and **Simplified Chinese** (`zh-CN`).
+Shipped languages: **English** (source and fallback), **Spanish** (`es`), **Russian** (`ru`), **Simplified Chinese** (`zh-CN`) and **Traditional Chinese** (`zh-TW`).
 
 ## 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`: [Spanish](./translations/es.md), [Russian](./translations/ru.md), [Simplified Chinese](./translations/zh-CN.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`: [Spanish](./translations/es.md), [Russian](./translations/ru.md), [Simplified Chinese](./translations/zh-CN.md), [Traditional Chinese](./translations/zh-TW.md). Read it before translating, and add a term there when you settle on one.

docs/translations/zh-TW.md

@@ -0,0 +1,36 @@
+# Traditional Chinese (`zh-TW`)
+
+Catalog: `src/i18n/locales/zh-TW.json`. General rules: [TRANSLATORS.md](../TRANSLATORS.md).
+
+Sources: caxer (#724), tbdavid2019 (#652), and the zh-CN catalog credited to abiyeenzo (#914) and EDIT-Aeterna (#979). The remaining entries were seeded with OpenCC s2twp and edited for Taiwan usage.
+
+## Style
+
+- Use Traditional characters and Taiwan terminology. Prefer short, neutral instructions: 「點選地圖」、「儲存金鑰」.
+- Use full-width Chinese punctuation and 「」 for quotations. Keep `·`, `…`, provider names, codes and placeholders unchanged.
+- Separate Chinese from Latin letters and numbers with a space: 「AIS 船舶」、「24 小時」. Keep unit symbols unchanged: km, m, km/h, m/s, kn, ft, MW, °, %.
+- Chinese labels have no uppercase variant. Keep button labels short and avoid splitting short words across lines.
+- Browser tags with Hant or TW/HK/MO select this Taiwan catalog. Explicit Hans selects Simplified Chinese, including Hans-TW. This is not a separate Hong Kong localization.
+
+## Plurals
+
+`Intl.PluralRules('zh-TW')` uses only `other`. Keep suitable measure words: 「{count} 架飛機」、「{count} 艘船」、「{count} 個金鑰」.
+
+## Taiwan terminology
+
+| English              | Taiwan                | Mainland            |
+| -------------------- | --------------------- | ------------------- |
+| data / information   | 資料 / 資訊           | 数据 / 信息         |
+| file / folder        | 檔案 / 資料夾         | 文件 / 文件夹       |
+| settings / save      | 設定 / 儲存           | 设置 / 保存         |
+| API key / token      | API 金鑰 / 權杖       | API 密钥 / 令牌     |
+| live / load          | 即時 / 載入           | 实时 / 加载         |
+| camera / video       | 攝影機 / 影片         | 摄像头 / 视频       |
+| network / link       | 網路 / 連結           | 网络 / 链接         |
+| image / imagery      | 圖像 / 影像           | 图像 / 影像         |
+| click / double-click | 點選 / 按兩下         | 点击 / 双击         |
+| response / timeout   | 回應 / 逾時           | 响应 / 超时         |
+| layer / data layer   | 圖層 / 資料圖層       | 图层 / 数据图层     |
+| cockpit / context    | 駕駛艙 / 態勢         | 座舱 / 态势         |
+| air quality          | 空氣品質              | 空气质量            |
+| transit / bikeshare  | 大眾運輸 / 公共自行車 | 公共交通 / 共享单车 |