@@ -0,0 +1,14 @@
+---
+'@objectstack/spec': minor
+---
+
+fix(spec/system): the platform locale table reads the script-subtag Chinese spellings, so a `zh-Hant-TW` / `zh-Hant-HK` reader gets a registered `zh-Hant` bundle instead of Simplified Chinese
+
+Clause-②: yes (widening)
+Metadata-protocol: semantic
+
+`PLATFORM_LOCALE_READ_ALIASES` (`@objectstack/spec/system`) gains five rows, one for the script-subtag spelling of each regional Chinese alias: `zh-Hans-CN` and `zh-Hans-SG` read as `zh-Hans`; `zh-Hant-TW`, `zh-Hant-HK` and `zh-Hant-MO` read as `zh-Hant`. `platformLocaleTagOf` answers them (case-insensitively, as for every row), and `PlatformLocaleReadAlias` gains the five literal keys.
+
+What changes for a reader: browsers and operating systems send these spellings. `resolveBundleLocale` and `resolveLocaleAmong` (and so `resolveLocale` and `resolveOfferedLocale` in `@objectstack/core`) now map them through the table before the base-language step, so over a bundle that holds both scripts a `zh-Hant-TW`, `zh-Hant-HK` or `zh-Hant-MO` request reaches the `zh-Hant` key and a `zh-Hans-CN` or `zh-Hans-SG` request reaches the Simplified key (`zh-CN`, `zh-Hans` or a bare `zh`), whatever order the keys were registered in. Before, the first registered `zh-*` key answered them, and over `{ zh, zh-Hant }` a `zh-Hant-TW` request got the bare `zh` (Simplified) key. The table step maps each registered key through the table too, so a bundle key or offered code spelled `zh-Hant-TW` / `zh-Hans-CN` now counts as its script for every request the table reads as that script: `zh-TW` or `zh-Hant` over `[en, zh-CN, zh-Hant-TW]` gets `zh-Hant-TW` (before: `zh-CN`), `zh-CN` over `[en, zh-Hant, zh-Hans-CN]` gets `zh-Hans-CN` (before: `zh-Hant`), and `zh-Hant-TW` over `[en, zh, zh-Hant-HK]` gets `zh-Hant-HK` (before: `zh`). Setup's default-language options (`localization.locale`) name the five codes from the table (`zh-Hant-TW` is 繁體中文, `zh-Hans-CN` is 简体中文) where they used the runtime's display name (中文（繁體，台灣）), and a stored `zh-Hant-TW` default now shows selected on the 繁體中文 option: where the deployment listed `zh-CN` before `zh-Hant`, it used to take the place of the 简体中文 option. The values Setup accepts are unchanged.
+
+Unchanged: the list stays closed. Only these five spellings are added; a script-subtag spelling without a row (`zh-Hant-US`) and every other code the table does not name (`pt-PT`, `en-GB`, `es-419`) answer `undefined` and fall back through base language and variant expansion exactly as before. With no registered key of the requested script, a script-subtag request still reaches the other script's key, as before. No call that matched before stops matching.
@@ -163,33 +163,48 @@ The rule:
 - **Adding or removing a language** is a change to the table, followed by one
   backfill of every surface. Nothing else declares the list.
 
-**Read aliases.** Codes that stored values already carry keep resolving:
+**Read aliases.** Codes that stored values already carry, and the
+script-subtag spellings browsers and operating systems send, keep resolving:
 `PLATFORM_LOCALE_READ_ALIASES` maps each to a table tag, and
-`platformLocaleTagOf(code)` answers the table tag a stored code means.
+`platformLocaleTagOf(code)` answers the table tag a code means.
 
-| Stored code | Reads as |
+| Code | Reads as |
 |:--|:--|
-| `zh`, `zh-CN`, `zh-SG` | `zh-Hans` |
-| `zh-TW`, `zh-HK`, `zh-MO` | `zh-Hant` |
+| `zh`, `zh-CN`, `zh-SG`, `zh-Hans-CN`, `zh-Hans-SG` | `zh-Hans` |
+| `zh-TW`, `zh-HK`, `zh-MO`, `zh-Hant-TW`, `zh-Hant-HK`, `zh-Hant-MO` | `zh-Hant` |
 | `ja-JP` | `ja` |
 | `es-ES` | `es` |
 | `pt` | `pt-BR` |
 | `en-US` | `en` |
 
 A table tag answers itself, the match ignores case (`zh-cn` reads as
-`zh-Hans`), and any other code answers `undefined`: no region fallback is
-guessed, so `pt-PT` is not `pt-BR`. New writes use the table's tags. The
+`zh-Hans`), and any other code answers `undefined`. The list is closed and is
+read row by row, never as a pattern, so no region or script fallback is
+guessed: `pt-PT` is not `pt-BR`, and a script-subtag spelling without a row
+(`zh-Hant-US`) answers `undefined` too. New writes use the table's tags. The
 examples on this page that spell `zh-CN` stay valid, because `zh-CN` is a read
 alias of `zh-Hans`.
 
 `platformLocaleTagOf` answers which table language a code *means*; the
-fallback ladder below answers which key of a bundle *serves* a request. A
-reader that uses both maps the code first and then resolves the table tag
-against the bundle, so they do not contradict each other: `pt` means `pt-BR`,
-and a request for `pt-BR` may still be served by a bundle's `pt` key. The
-ladder alone cannot tell the two Chinese scripts apart: once a bundle holds
-both `zh-Hans` and `zh-Hant`, a request for `zh` or `zh-CN` is answered by key
-order (`zh-Hant` when that key comes first), where the table says `zh-Hans`.
+fallback ladder answers which key of a bundle *serves* a request. The ladder is
+one function, `resolveLocaleAmong`: `resolveBundleLocale` runs it over a
+bundle's keys, and core's `resolveLocale` is the same function. Its steps are
+exact match, case-insensitive match, then the **same table language**, then
+base language, then the first registered variant. The table-language step maps
+the request through `platformLocaleTagOf` and takes the key spelled as that
+table tag, else the first key the table maps to it, so the two answers never
+contradict each other: `pt` means `pt-BR`, and a request for `pt-BR` is served
+by a bundle's `pt` key. A bundle holding both scripts answers `zh`, `zh-CN` and
+`zh-Hans-CN` with its Simplified key and `zh-TW` and `zh-Hant-TW` with its
+Traditional one, whatever order the keys were registered in.
+
+Two kinds of request still go to the base-language and first-variant steps,
+where registration order decides. A code the table does not name skips the
+table step: over keys registered as `en`, `zh-CN`, `zh-Hant` a `zh-Hant-US`
+request gets `zh-CN`, and with `zh-Hant` registered before `zh-CN` it gets
+`zh-Hant`. A request whose table language has no key falls through the same
+way: `zh-TW` over `en`, `zh-CN` gets `zh-CN`, because a related language beats
+none.
 
 ### Locale Fallback
 
 
@@ -315,6 +315,30 @@ describe('resolveLocale and resolveBundleLocale — one shared case list', () =>
         ['zh-SG', ['en', 'zh-Hant', 'zh-CN'], 'zh-CN'],
         ['zh-Hans', ['en', 'zh-Hant', 'zh-CN'], 'zh-CN'],
         ['zh-TW', ['en', 'zh', 'zh-Hant'], 'zh-Hant'],
+        // The script-subtag spellings a browser or OS sends are read aliases too.
+        ['zh-Hant-TW', ['en', 'zh-CN', 'zh-Hant'], 'zh-Hant'],
+        ['zh-Hant-TW', ['en', 'zh-Hant', 'zh-CN'], 'zh-Hant'],
+        ['zh-Hant-HK', ['en', 'zh-CN', 'zh-Hant'], 'zh-Hant'],
+        ['zh-Hant-HK', ['en', 'zh-Hant', 'zh-CN'], 'zh-Hant'],
+        ['zh-Hant-MO', ['en', 'zh-CN', 'zh-Hant'], 'zh-Hant'],
+        ['zh-Hant-MO', ['en', 'zh-Hant', 'zh-CN'], 'zh-Hant'],
+        ['zh-Hans-CN', ['en', 'zh-CN', 'zh-Hant'], 'zh-CN'],
+        ['zh-Hans-CN', ['en', 'zh-Hant', 'zh-CN'], 'zh-CN'],
+        ['zh-Hans-SG', ['en', 'zh-CN', 'zh-Hant'], 'zh-CN'],
+        ['zh-Hans-SG', ['en', 'zh-Hant', 'zh-CN'], 'zh-CN'],
+        ['ZH-HANT-tw', ['en', 'zh-CN', 'zh-Hant'], 'zh-Hant'],
+        ['zh-Hant-TW', ['en', 'zh', 'zh-Hant'], 'zh-Hant'],
+        // ...and so are keys spelled that way: a key counts as the script it names.
+        ['zh-TW', ['en', 'zh-CN', 'zh-Hant-TW'], 'zh-Hant-TW'],
+        ['zh-TW', ['en', 'zh-Hant-TW', 'zh-CN'], 'zh-Hant-TW'],
+        ['zh-Hant', ['en', 'zh-CN', 'zh-Hant-TW'], 'zh-Hant-TW'],
+        ['zh-Hant', ['en', 'zh-Hant-TW', 'zh-CN'], 'zh-Hant-TW'],
+        ['zh-CN', ['en', 'zh-Hant', 'zh-Hans-CN'], 'zh-Hans-CN'],
+        ['zh-CN', ['en', 'zh-Hans-CN', 'zh-Hant'], 'zh-Hans-CN'],
+        ['zh-Hant-TW', ['en', 'zh', 'zh-Hant-HK'], 'zh-Hant-HK'],
+        ['zh-Hant-TW', ['en', 'zh-Hant-HK', 'zh'], 'zh-Hant-HK'],
+        // One script registered: a related language still beats none.
+        ['zh-Hant-TW', ['en', 'zh-CN'], 'zh-CN'],
         // Today's alias-spelled bundles keep answering.
         ['ja', ['en', 'zh-CN', 'ja-JP', 'es-ES'], 'ja-JP'],
         ['es', ['en', 'zh-CN', 'ja-JP', 'es-ES'], 'es-ES'],
@@ -344,6 +368,19 @@ describe('resolveLocale and resolveBundleLocale — one shared case list', () =>
         expect(i18n.t('settings', 'zh-HK')).toBe('設定');
         expect(i18n.t('settings', 'zh')).toBe('设置');
     });
+
+    it.each<[order: string, loadOrder: string[]]>([
+        ['Simplified loaded first', ['zh-CN', 'zh-Hant']],
+        ['Traditional loaded first', ['zh-Hant', 'zh-CN']],
+    ])('a script-subtag reader of the in-memory service gets its own script (%s)', (_order, loadOrder) => {
+        const text: Record<string, string> = { 'zh-CN': '设置', 'zh-Hant': '設定' };
+        const i18n = createMemoryI18n();
+        i18n.loadTranslations('en', { settings: 'Settings' });
+        for (const locale of loadOrder) i18n.loadTranslations(locale, { settings: text[locale] });
+        expect(i18n.t('settings', 'zh-Hant-TW')).toBe('設定');
+        expect(i18n.t('settings', 'zh-Hant-HK')).toBe('設定');
+        expect(i18n.t('settings', 'zh-Hans-CN')).toBe('设置');
+    });
 });
 
 describe('createMemoryI18n locale fallback', () => {
 
@@ -1048,10 +1048,11 @@ describe('locale fallback resolution (BCP-47)', () => {
 
 // The platform locale table's read aliases decide which key serves a request
 // before any base-language or first-variant guess, so a Traditional reader
-// (`zh-TW`, `zh-HK`, `zh-MO`) reaches a `zh-Hant` key and a Simplified one
-// reaches `zh-CN` whatever order the bundle registered them in. Core's
-// `resolveLocale` is `resolveLocaleAmong`; its own suite runs one case list
-// against both resolvers.
+// (`zh-TW`, `zh-HK`, `zh-MO`, or the script-subtag `zh-Hant-TW` a browser
+// sends) reaches a `zh-Hant` key and a Simplified one reaches `zh-CN` whatever
+// order the bundle registered them in. Core's `resolveLocale` is
+// `resolveLocaleAmong`; its own suite runs one case list against both
+// resolvers.
 describe('resolveBundleLocale — the platform table language step', () => {
   const orders: Array<[string, Record<string, unknown>]> = [
     ['Simplified first', { en: {}, 'zh-CN': {}, 'zh-Hant': {} }],
@@ -1060,11 +1061,17 @@ describe('resolveBundleLocale — the platform table language step', () => {
 
   for (const [name, bundle] of orders) {
     describe(name, () => {
-      it.each(['zh-TW', 'zh-HK', 'zh-MO', 'zh-tw', 'zh-Hant'])('%s reaches zh-Hant', (requested) => {
+      it.each([
+        'zh-TW', 'zh-HK', 'zh-MO', 'zh-tw', 'zh-Hant',
+        'zh-Hant-TW', 'zh-Hant-HK', 'zh-Hant-MO', 'ZH-HANT-tw',
+      ])('%s reaches zh-Hant', (requested) => {
         expect(resolveBundleLocale(bundle, requested)).toBe('zh-Hant');
       });
 
-      it.each(['zh-CN', 'zh', 'zh-SG', 'zh-Hans', 'zh-cn'])('%s reaches zh-CN', (requested) => {
+      it.each([
+        'zh-CN', 'zh', 'zh-SG', 'zh-Hans', 'zh-cn',
+        'zh-Hans-CN', 'zh-Hans-SG', 'zh-hans-cn',
+      ])('%s reaches zh-CN', (requested) => {
         expect(resolveBundleLocale(bundle, requested)).toBe('zh-CN');
       });
     });
@@ -1079,6 +1086,24 @@ describe('resolveBundleLocale — the platform table language step', () => {
   it('runs before the base-language step: a bare `zh` key is Simplified', () => {
     expect(resolveBundleLocale({ zh: {}, 'zh-Hant': {} }, 'zh-TW')).toBe('zh-Hant');
     expect(resolveBundleLocale({ 'zh-Hant': {}, zh: {} }, 'zh-CN')).toBe('zh');
+    expect(resolveBundleLocale({ zh: {}, 'zh-Hant': {} }, 'zh-Hant-TW')).toBe('zh-Hant');
+    expect(resolveBundleLocale({ 'zh-Hant': {}, zh: {} }, 'zh-Hans-CN')).toBe('zh');
+    expect(resolveBundleLocale({ en: {}, zh: {}, 'zh-Hant-HK': {} }, 'zh-Hant-TW')).toBe('zh-Hant-HK');
+    expect(resolveBundleLocale({ en: {}, 'zh-Hant-HK': {}, zh: {} }, 'zh-Hant-TW')).toBe('zh-Hant-HK');
+  });
+
+  it('reads a key spelled with a script subtag as the script it names, in either registration order', () => {
+    for (const keys of [['en', 'zh-CN', 'zh-Hant-TW'], ['en', 'zh-Hant-TW', 'zh-CN']]) {
+      const bundle = Object.fromEntries(keys.map((code) => [code, {}]));
+      expect(resolveBundleLocale(bundle, 'zh-TW')).toBe('zh-Hant-TW');
+      expect(resolveBundleLocale(bundle, 'zh-Hant')).toBe('zh-Hant-TW');
+    }
+    for (const keys of [['en', 'zh-Hant', 'zh-Hans-CN'], ['en', 'zh-Hans-CN', 'zh-Hant']]) {
+      const bundle = Object.fromEntries(keys.map((code) => [code, {}]));
+      expect(resolveBundleLocale(bundle, 'zh-CN')).toBe('zh-Hans-CN');
+    }
+    // One script registered: a related language still beats none.
+    expect(resolveBundleLocale({ en: {}, 'zh-CN': {} }, 'zh-Hant-TW')).toBe('zh-CN');
   });
 
   it('keeps the alias-spelled bundles of today: ja → ja-JP, es → es-ES, en → en-US', () => {
 
@@ -61,6 +61,12 @@ describe('PLATFORM_LOCALE_READ_ALIASES: stored codes keep resolving', () => {
     ['zh-TW', 'zh-Hant'],
     ['zh-HK', 'zh-Hant'],
     ['zh-MO', 'zh-Hant'],
+    // The script-subtag spellings of the five regional aliases (#30618).
+    ['zh-Hans-CN', 'zh-Hans'],
+    ['zh-Hans-SG', 'zh-Hans'],
+    ['zh-Hant-TW', 'zh-Hant'],
+    ['zh-Hant-HK', 'zh-Hant'],
+    ['zh-Hant-MO', 'zh-Hant'],
     ['ja-JP', 'ja'],
     ['es-ES', 'es'],
     ['pt', 'pt-BR'],
@@ -72,13 +78,15 @@ describe('PLATFORM_LOCALE_READ_ALIASES: stored codes keep resolving', () => {
     expect(platformLocaleTagOf(code)).toBe(tag);
   });
 
-  it('the map is exactly those ten aliases', () => {
+  it('the map is exactly those fifteen aliases', () => {
     expect(PLATFORM_LOCALE_READ_ALIASES).toEqual(Object.fromEntries(ALIASES));
   });
 
-  it('the map is typed on its ten literal keys: an unlisted code does not index it as defined', () => {
+  it('the map is typed on its fifteen literal keys: an unlisted code does not index it as defined', () => {
     const zhCN: 'zh-Hans' = PLATFORM_LOCALE_READ_ALIASES['zh-CN'];
     expect(zhCN).toBe('zh-Hans');
+    const zhHantTW: 'zh-Hant' = PLATFORM_LOCALE_READ_ALIASES['zh-Hant-TW'];
+    expect(zhHantTW).toBe('zh-Hant');
     // @ts-expect-error `pt-PT` is not a read alias, so the index is not typed as a table tag.
     expect(PLATFORM_LOCALE_READ_ALIASES['pt-PT']).toBeUndefined();
   });
@@ -113,12 +121,19 @@ describe('platformLocaleTagOf', () => {
     ['EN', 'en'],
     ['en-us', 'en'],
     ['ja-jp', 'ja'],
+    ['ZH-HANS-cn', 'zh-Hans'],
+    ['zh-hans-sg', 'zh-Hans'],
+    ['ZH-HANT-tw', 'zh-Hant'],
+    ['zh-hant-hk', 'zh-Hant'],
+    ['Zh-Hant-Mo', 'zh-Hant'],
   ])('ignores case: %s reads as %s', (code, tag) => {
     expect(platformLocaleTagOf(code)).toBe(tag);
   });
 
-  // The list is closed: no region or script fallback is guessed.
-  it.each(['pt-PT', 'de-AT', 'en-GB', 'zh-Hans-CN', 'es-419', 'fr-CA', 'it', 'he', 'zh-Hant-TW'])(
+  // The list is closed: no region or script fallback is guessed. A
+  // script-subtag spelling without its own row (`zh-Hant-US`, `zh-Hans-US`)
+  // answers undefined too: the rows are read one by one, never as a pattern.
+  it.each(['pt-PT', 'de-AT', 'en-GB', 'es-419', 'fr-CA', 'it', 'he', 'zh-Hant-US', 'zh-Hans-US'])(
     'a code the table and the aliases do not list, %s, answers undefined',
     (code) => {
       expect(platformLocaleTagOf(code)).toBeUndefined();
 
@@ -59,11 +59,18 @@ export const PLATFORM_LOCALE_TAGS: readonly PlatformLocaleTag[] = Object.freeze(
 );
 
 /**
- * Read aliases: a code that stored values already carry, mapped to the table
- * tag it means. Reads only: a new write uses the table tag itself.
+ * Read aliases: a code that stored values already carry, or that a browser or
+ * operating system sends, mapped to the table tag it means. Reads only: a new
+ * write uses the table tag itself.
+ *
+ * Each regional Chinese alias also has a row for its script-subtag spelling,
+ * which names the table tag outright: `zh-Hans-CN` and `zh-Hans-SG` read as
+ * `zh-Hans`, `zh-Hant-TW`, `zh-Hant-HK` and `zh-Hant-MO` as `zh-Hant`.
  *
  * The list is closed. A code it does not name is not guessed at, so there is
- * no region fallback here (`pt-PT` is not `pt-BR`, `zh-Hans-CN` is not listed).
+ * no region or script fallback here: `pt-PT` is not `pt-BR`, and a
+ * script-subtag spelling without a row (`zh-Hant-US`) answers nothing, because
+ * the rows are read one by one, never as a pattern.
  * Frozen.
  */
 export const PLATFORM_LOCALE_READ_ALIASES = Object.freeze({
@@ -73,6 +80,12 @@ export const PLATFORM_LOCALE_READ_ALIASES = Object.freeze({
   'zh-TW': 'zh-Hant',
   'zh-HK': 'zh-Hant',
   'zh-MO': 'zh-Hant',
+  // The script-subtag spellings of the five regional aliases above (#30618).
+  'zh-Hans-CN': 'zh-Hans',
+  'zh-Hans-SG': 'zh-Hans',
+  'zh-Hant-TW': 'zh-Hant',
+  'zh-Hant-HK': 'zh-Hant',
+  'zh-Hant-MO': 'zh-Hant',
   'ja-JP': 'ja',
   'es-ES': 'es',
   pt: 'pt-BR',
@@ -109,8 +122,9 @@ const TAG_BY_FOLDED_CODE: ReadonlyMap<string, PlatformLocaleTag> = new Map<strin
  * language, first variant). Its table-language step asks this function of
  * both the requested code and each key, so the two never contradict: `pt`
  * means `pt-BR`, and a request for `pt-BR` may still be served by a bundle's
- * `pt` key; a bundle holding both scripts answers `zh` and `zh-CN` with its
- * Simplified key and `zh-TW` with its Traditional one, in any key order.
+ * `pt` key; a bundle holding both scripts answers `zh`, `zh-CN` and
+ * `zh-Hans-CN` with its Simplified key and `zh-TW` and `zh-Hant-TW` with its
+ * Traditional one, in any key order.
  */
 export function platformLocaleTagOf(code: unknown): PlatformLocaleTag | undefined {
   if (typeof code !== 'string') return undefined;