@@ -0,0 +1,12 @@
+---
+'@object-ui/console': patch
+---
+
+fix(console): a language picked on the sign-in page reaches date and number formatting
+
+Clause-②: no
+Metadata-protocol: none
+
+A user with no stored `sys_user.locale` who picked 中文 on the sign-in page saw every list grid's date cells as `Nov 18` beside Chinese headers, on every page load. `<html lang>` already followed the pick, but `LocalizationFetchProvider` reads `GET /api/v1/auth/me/localization` through `sharedGetJson`'s bare `fetch`, so that one read never carried the `<html lang>` `Accept-Language` every other console API call carries; the server answered its `Accept-Language` rung in the browser's language, and `useDisplayLocale` formats with that answer.
+
+When the device holds an explicit language choice, the read now states that language as its `Accept-Language`, and reads again when the choice changes. The server's rung order is unchanged (a stored `sys_user.locale` still answers first), and so is `useDisplayLocale`'s precedence. With no choice on the device the browser's header still goes out, so a first visit's language seed and this read keep sharing one request.
@@ -17,7 +17,14 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import { render, screen, waitFor } from '@testing-library/react';
 import { act } from 'react';
-import { LOCALE_SEED_STORAGE_KEY, LOCALE_STORAGE_KEY, useDisplayLocale, useLocalization } from '@object-ui/i18n';
+import {
+  I18nProvider,
+  LOCALE_SEED_STORAGE_KEY,
+  LOCALE_STORAGE_KEY,
+  useDisplayLocale,
+  useLocalization,
+  useObjectTranslation,
+} from '@object-ui/i18n';
 import { formatDate, formatDateTime, setDisplayTimeZone } from '@object-ui/core';
 import { notifyDataChanged } from '@object-ui/react';
 // Test-only and off the `@object-ui/types` barrel; the vitest alias makes this
@@ -358,4 +365,100 @@ describe('LocalizationFetchProvider', () => {
       expect(fetchMock()).toHaveBeenCalledTimes(1);
     });
   });
+
+  describe('states the device\'s chosen language (objectstack#27625)', () => {
+    const fetchMock = () => globalThis.fetch as never as ReturnType<typeof vi.fn>;
+    /** The `Accept-Language` the Nth request stated; `null` = none, the browser's own goes out. */
+    const statedOn = (n: number) =>
+      (fetchMock().mock.calls[n]?.[1]?.headers as Record<string, string> | undefined)?.['Accept-Language'] ?? null;
+
+    let switchTo: (code: string) => Promise<void> = async () => {};
+
+    /** The date face a grid cell paints, plus a handle on the language switch. */
+    function DisplayProbe() {
+      const { changeLanguage } = useObjectTranslation();
+      switchTo = changeLanguage;
+      const locale = useDisplayLocale();
+      return (
+        <span data-testid="display">
+          {`${locale}|${formatDate('2026-10-11', undefined, { locale, alwaysShowYear: true })}`}
+        </span>
+      );
+    }
+
+    function renderUnderLanguage(language: string) {
+      return render(
+        <I18nProvider config={{ defaultLanguage: language, detectBrowserLanguage: false }}>
+          <LocalizationFetchProvider endpoint={ENDPOINT}>
+            <DisplayProbe />
+          </LocalizationFetchProvider>
+        </I18nProvider>,
+      );
+    }
+
+    beforeEach(() => { window.localStorage.clear(); authUser = { id: 'u1' }; });
+    afterEach(() => {
+      authUser = null;
+      window.localStorage.clear();
+      resetInflightGetsForTesting();
+    });
+
+    it('a language picked before sign-in is the one the read states, and the dates follow it', async () => {
+      // The sign-in page's pick: the explicit-choice slot, no `sys_user.locale`.
+      window.localStorage.setItem(LOCALE_STORAGE_KEY, 'zh');
+      // The server answers the `Accept-Language` rung with what it was told.
+      fetchMock().mockImplementation(async (_url: string, init: RequestInit) =>
+        ok({
+          authenticated: true,
+          currency: null,
+          locale: (init.headers as Record<string, string>)['Accept-Language'] ?? 'en-US',
+          timezone: 'UTC',
+        }),
+      );
+
+      renderUnderLanguage('zh');
+
+      await waitFor(() => expect(screen.getByTestId('display')).toHaveTextContent('zh|2026年10月11日'));
+      expect(statedOn(0)).toBe('zh');
+      expect(fetchMock()).toHaveBeenCalledTimes(1);
+    });
+
+    it('with no choice on this device, the read states nothing and the browser\'s header goes out', async () => {
+      fetchMock().mockResolvedValue(ok({ authenticated: true, currency: null, locale: 'en-US', timezone: 'UTC' }));
+
+      renderUnderLanguage('en');
+
+      await waitFor(() => expect(fetchMock()).toHaveBeenCalledTimes(1));
+      expect(statedOn(0)).toBeNull();
+    });
+
+    it('a change of the chosen language reads again, stating the new one', async () => {
+      window.localStorage.setItem(LOCALE_STORAGE_KEY, 'en');
+      fetchMock()
+        .mockResolvedValueOnce(ok({ authenticated: true, currency: null, locale: 'en', timezone: 'UTC' }))
+        .mockResolvedValueOnce(ok({ authenticated: true, currency: null, locale: 'zh', timezone: 'UTC' }));
+
+      renderUnderLanguage('en');
+      await waitFor(() => expect(screen.getByTestId('display')).toHaveTextContent('en|Oct 11, 2026'));
+
+      await act(async () => { await switchTo('zh'); });
+
+      await waitFor(() => expect(screen.getByTestId('display')).toHaveTextContent('zh|2026年10月11日'));
+      expect(fetchMock()).toHaveBeenCalledTimes(2);
+      expect(statedOn(0)).toBe('en');
+      expect(statedOn(1)).toBe('zh');
+    });
+
+    it('a stored sys_user.locale still wins over the stated language', async () => {
+      window.localStorage.setItem(LOCALE_STORAGE_KEY, 'zh');
+      // The column's rung answers first, whatever the header says.
+      fetchMock().mockResolvedValue(ok({ authenticated: true, currency: null, locale: 'de-DE', timezone: 'UTC' }));
+
+      renderUnderLanguage('zh');
+
+      await waitFor(() => expect(screen.getByTestId('display').textContent).toMatch(/^de-DE\|/));
+      expect(screen.getByTestId('display').textContent).not.toContain('年');
+      expect(statedOn(0)).toBe('zh');
+    });
+  });
 });
@@ -45,9 +45,35 @@
  * profile page's. That re-read starts after the write has settled, and it does
  * not join a request still in flight from before it (the shared in-flight
  * registry would hand back the stale answer), so it is the one that lands.
+ *
+ * ## State the device's chosen language (objectstack#27625)
+ *
+ * Every other console API call carries the active UI language as its
+ * `Accept-Language` (`createAuthenticatedFetch` stamps `<html lang>`), but this
+ * read goes through `sharedGetJson`'s bare `fetch`, so it carried the BROWSER's
+ * header instead. A user with no `sys_user.locale` who picked 中文 on the
+ * sign-in page therefore got the `Accept-Language` rung answered in the
+ * browser's language, and every date cell said `Nov 18` under Chinese headers,
+ * on every load.
+ *
+ * So when the device holds an explicit language choice, this read states that
+ * language. The server's rungs are unchanged: a stored `sys_user.locale` still
+ * answers first, and the header only decides the rung below it. Without a
+ * choice the browser's header stays: that is exactly the boot on which
+ * `seedTenantLanguage()` asks this endpoint too, and the two share one request
+ * only while their headers match (objectui#5544). The stated language is part
+ * of the request, so a change of it reads again, and the new read cannot join
+ * one still in flight under the old language: the in-flight key includes the
+ * headers.
  */
 import { useEffect, useState } from 'react';
-import { LocalizationProvider, cacheLanguageSeed, type LocalizationValue } from '@object-ui/i18n';
+import {
+  LocalizationProvider,
+  cacheLanguageSeed,
+  readStoredLanguage,
+  useObjectTranslation,
+  type LocalizationValue,
+} from '@object-ui/i18n';
 import { getSessionOwnerChangeCount, useAuth } from '@object-ui/auth';
 import { useDataInvalidation } from '@object-ui/react';
 import {
@@ -87,6 +113,10 @@ export function LocalizationFetchProvider({
   const userId = user?.id ? String(user.id) : undefined;
   // Bumps on every write to the signed-in user's own row (objectstack#27498).
   const userRowWrites = useDataInvalidation(userId ? 'sys_user' : undefined, userId);
+  // The device's chosen UI language, stated as this read's `Accept-Language`;
+  // none chosen, the browser's own header goes out (objectstack#27625).
+  const { language } = useObjectTranslation();
+  const statedLanguage = readStoredLanguage() ? language : undefined;
 
   useEffect(() => {
     let cancelled = false;
@@ -113,7 +143,10 @@ export function LocalizationFetchProvider({
           // resolving one of them empty.
           const json = await sharedGetJson<MeLocalizationResponse>(endpoint, {
             credentials: 'include',
-            headers: { Accept: 'application/json' },
+            headers: {
+              Accept: 'application/json',
+              ...(statedLanguage ? { 'Accept-Language': statedLanguage } : {}),
+            },
             signal: reread?.signal,
           });
           // Refresh the UI-language seed cache (objectui#4035) — the
@@ -164,7 +197,7 @@ export function LocalizationFetchProvider({
       cancelled = true;
       reread?.abort();
     };
-  }, [endpoint, userRowWrites]);
+  }, [endpoint, userRowWrites, statedLanguage]);
 
   return <LocalizationProvider value={value}>{children}</LocalizationProvider>;
 }