fix(settings): keep the language and save settings one after the other

src/App.jsx

@@ -28,7 +28,7 @@ import {logout} from './utils/api.js';
 function App() {
     const {t} = useTranslation();
     const [isAuthenticated, setIsAuthenticated] = useState(false);
-    const {appearance, syncAppearance, resetAppearance} = usePreferences();
+    const {appearance, syncPreferences, resetAppearance} = usePreferences();
 
     // Hooks for routing
     const navigate = useNavigate();
@@ -42,8 +42,8 @@ function App() {
 
     // On login and on page load; the cached look shows until Auth answers.
     useEffect(() => {
-        if (isAuthenticated) syncAppearance();
-    }, [isAuthenticated, syncAppearance]);
+        if (isAuthenticated) syncPreferences();
+    }, [isAuthenticated, syncPreferences]);
 
     // Waits for Auth: a late logout answer would clear the cookies of a login that came after it.
     const handleLogout = async () => {

src/components/AppHeader.jsx

@@ -71,7 +71,16 @@ export default function AppHeader({isAuthenticated, onLogout}) {
         toast.error(t('NAV.VIEW_AS.ERROR'));
     };
 
-    const toggleLanguage = () => setLanguage(i18n.language === 'de' ? 'en' : 'de');
+    // Unsaved, the next login would switch back to Auth's language.
+    const toggleLanguage = async () => {
+        try {
+            const response = await setLanguage(i18n.language === 'de' ? 'en' : 'de');
+            if (response && !response.ok) toast.error(t('SETTINGS.ERROR_SAVE'));
+        } catch (err) {
+            console.error('Language save error:', err);
+            toast.error(t('INFO.ERROR.NETWORK_FAILURE'));
+        }
+    };
     const toggleTheme = () => setDarkMode(!isDarkMode);
     const ThemeIcon = isDarkMode ? Sun : Moon;
 

src/components/AppHeader.test.jsx

@@ -2,14 +2,18 @@
 import {afterEach, describe, expect, it, vi} from 'vitest';
 import {cleanup, fireEvent, render, screen} from '@testing-library/react';
 import {MemoryRouter} from 'react-router-dom';
+import {toast} from 'sonner';
+import {useTranslation} from 'react-i18next';
 import AppHeader from './AppHeader.jsx';
 import {PreferencesProvider} from '../context/PreferencesContext.jsx';
 
 vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
+vi.mock('sonner', () => ({toast: {success: vi.fn(), error: vi.fn()}}));
 
 afterEach(() => {
     cleanup();
     localStorage.clear();
+    useTranslation().i18n.language = 'de';
 });
 
 const loggedInAs = (me) => {
@@ -27,6 +31,19 @@ const loggedInAs = (me) => {
 const openMenu = () => fireEvent.keyDown(screen.getByRole('button', {name: 'NAV.MENU'}), {key: 'Enter'});
 
 describe('AppHeader', () => {
+    it('says so when Auth refuses the language switch', async () => {
+        loggedInAs({role: 'USER', activeRole: 'USER', settings: {language: 'de'}});
+        fetch.mockImplementation(async (url, init) => (init?.method === 'PUT'
+            ? {ok: false, status: 500, json: async () => ({})}
+            : {ok: true, status: 200, json: async () => ({role: 'USER', activeRole: 'USER', settings: {language: 'de'}})}));
+
+        await screen.findByRole('button', {name: 'NAV.MENU'});
+        openMenu();
+        fireEvent.click(await screen.findByRole('menuitem', {name: /NAV.LANGUAGE/}));
+
+        await vi.waitFor(() => expect(toast.error).toHaveBeenCalledWith('SETTINGS.ERROR_SAVE'));
+    });
+
     // jsdom applies no media queries, so the test hides the name the way the 380px breakpoint does.
     it('keeps a name on the home link when a narrow phone hides the app name', () => {
         render(

src/context/PreferencesContext.jsx

@@ -4,11 +4,13 @@ import {
     applyAppearance,
     cacheAppearance,
     DEFAULT_APPEARANCE,
-    loadAppearance,
+    loadPreferences,
     normalizeAppearance,
     readCachedAppearance,
     saveAppearance,
 } from '../utils/appearance.js';
+import {hasSession} from '../utils/auth.js';
+import {LANGUAGES, saveSettings} from '../utils/settings.js';
 
 const DARK_MODE_STORAGE_KEY = 'tbp_dark_mode';
 // The --background of style.css; the installed app paints its title bar in this color.
@@ -51,21 +53,29 @@ export function PreferencesProvider({children}) {
         cacheAppearance(appearance);
     }, [appearance]);
 
-    const syncAppearance = useCallback(() => {
+    // Grows on every language pick, so a load that started before does not undo it.
+    const languagePicks = useRef(0);
+
+    const syncPreferences = useCallback(() => {
         const started = generation.current;
+        const picksBefore = languagePicks.current;
         syncing.current = (async () => {
             try {
-                const loaded = await loadAppearance();
-                if (loaded && generation.current === started) {
-                    savedAppearance.current = loaded;
-                    setAppearanceState(normalizeAppearance({...loaded, ...pendingChanges.current}));
+                const loaded = await loadPreferences();
+                if (loaded?.appearance && generation.current === started) {
+                    savedAppearance.current = loaded.appearance;
+                    setAppearanceState(normalizeAppearance({...loaded.appearance, ...pendingChanges.current}));
+                }
+                if (LANGUAGES.includes(loaded?.language) && languagePicks.current === picksBefore
+                    && loaded.language !== i18n.language) {
+                    i18n.changeLanguage(loaded.language);
                 }
             } catch (err) {
-                console.error('Appearance load error:', err);
+                console.error('Preferences load error:', err);
             }
         })();
         return syncing.current;
-    }, []);
+    }, [i18n]);
 
     /**
      * Applies the changed fields at once, then saves them to Auth after a running load and after the saves before
@@ -114,7 +124,17 @@ export function PreferencesProvider({children}) {
         setAppearanceState(DEFAULT_APPEARANCE);
     }, []);
 
-    const setLanguage = (lang) => i18n.changeLanguage(lang);
+    /**
+     * Applies the language at once and saves it to Auth while logged in.
+     *
+     * @return the fetch response, or null when logged out; rejects on a network error
+     */
+    const setLanguage = (lang) => {
+        languagePicks.current += 1;
+        i18n.changeLanguage(lang);
+        if (!hasSession()) return Promise.resolve(null);
+        return saveSettings({language: lang});
+    };
 
     return (
         <PreferencesContext.Provider
@@ -125,7 +145,7 @@ export function PreferencesProvider({children}) {
                 setLanguage,
                 appearance,
                 changeAppearance,
-                syncAppearance,
+                syncPreferences,
                 resetAppearance,
             }}
         >

src/context/PreferencesContext.test.jsx

@@ -3,7 +3,11 @@ import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
 import {act, cleanup, render} from '@testing-library/react';
 import {PreferencesProvider, usePreferences} from './PreferencesContext.jsx';
 
-vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
+const i18n = vi.hoisted(() => ({language: 'de'}));
+vi.mock('react-i18next', async () => {
+    const mock = await import('../test/i18n-mock.js');
+    return {...mock, useTranslation: () => ({t: mock.useTranslation().t, i18n})};
+});
 
 let preferences;
 function Spy() {
@@ -17,11 +21,67 @@ beforeEach(() => {
     document.head.innerHTML = '<meta name="theme-color" content="#09090b">';
 });
 
+beforeEach(() => {
+    i18n.language = 'de';
+    i18n.changeLanguage = vi.fn((lng) => { i18n.language = lng; });
+});
+
 afterEach(() => {
     cleanup();
     localStorage.clear();
 });
 
+const answerMe = (settings) => {
+    globalThis.fetch = vi.fn(async (url, init) => (init?.method === 'PUT'
+        ? {ok: true, status: 204}
+        : {ok: true, status: 200, json: async () => ({displayName: 'Lobo', settings})}));
+};
+
+describe('PreferencesProvider language', () => {
+    it('takes the language saved in Auth', async () => {
+        answerMe({language: 'en', useDarkTheme: true, publicProfile: false});
+        render(<PreferencesProvider><Spy/></PreferencesProvider>);
+
+        await act(() => preferences.syncPreferences());
+
+        expect(i18n.changeLanguage).toHaveBeenCalledWith('en');
+    });
+
+    it('keeps its own language while Auth has none', async () => {
+        answerMe({language: '', useDarkTheme: true, publicProfile: false});
+        render(<PreferencesProvider><Spy/></PreferencesProvider>);
+
+        await act(() => preferences.syncPreferences());
+
+        expect(i18n.changeLanguage).not.toHaveBeenCalled();
+    });
+
+    it('keeps a language picked while Auth was still answering', async () => {
+        answerMe({language: 'de', useDarkTheme: true, publicProfile: false});
+        render(<PreferencesProvider><Spy/></PreferencesProvider>);
+
+        await act(async () => {
+            const sync = preferences.syncPreferences();
+            preferences.setLanguage('en');
+            await sync;
+        });
+
+        expect(i18n.changeLanguage.mock.calls).toEqual([['en']]);
+    });
+
+    it('saves a picked language to Auth with the other settings unchanged', async () => {
+        localStorage.setItem('tbp_session', '1');
+        answerMe({language: 'de', useDarkTheme: true, publicProfile: true});
+        render(<PreferencesProvider><Spy/></PreferencesProvider>);
+
+        await act(() => preferences.setLanguage('en'));
+
+        const put = fetch.mock.calls.find(([, init]) => init?.method === 'PUT');
+        expect(put[0]).toMatch(/\/api\/users\/settings$/);
+        expect(JSON.parse(put[1].body)).toEqual({useDarkTheme: true, language: 'en', displayName: 'Lobo', publicProfile: true});
+    });
+});
+
 describe('PreferencesProvider theme color', () => {
     it('gives the installed app a light title bar in light mode and a dark one again in dark mode', () => {
         localStorage.setItem('tbp_dark_mode', 'false');

src/hooks/useSaveAppearance.test.jsx

@@ -121,7 +121,7 @@ describe('useSaveAppearance', () => {
         let sync;
         let save;
         act(() => {
-            sync = result.current.preferences.syncAppearance();
+            sync = result.current.preferences.syncPreferences();
         });
         act(() => {
             save = result.current.save({corners: 'round'});
@@ -149,7 +149,7 @@ describe('useSaveAppearance', () => {
 
         let sync;
         act(() => {
-            sync = result.current.preferences.syncAppearance();
+            sync = result.current.preferences.syncPreferences();
         });
         act(() => result.current.preferences.resetAppearance());
         await act(async () => {
@@ -209,7 +209,7 @@ describe('useSaveAppearance', () => {
         const {result} = renderSave();
 
         act(() => {
-            result.current.preferences.syncAppearance();
+            result.current.preferences.syncPreferences();
         });
         let save;
         act(() => {

src/i18n.js

@@ -1,12 +1,13 @@
 import i18n from 'i18next';
 import {initReactI18next} from 'react-i18next';
 import HttpBackend from 'i18next-http-backend';
+import {cacheLanguage, readCachedLanguage} from './utils/settings.js';
 
 
 i18n.use(HttpBackend)
     .use(initReactI18next)
     .init({
-        lng: 'de',
+        lng: readCachedLanguage() ?? 'de',
         fallbackLng: 'en',
         backend: {
             // A browser kept an old file without its Cache-Control and showed raw keys; a new URL per version avoids that.
@@ -17,4 +18,6 @@ i18n.use(HttpBackend)
         }
     });
 
+i18n.on('languageChanged', cacheLanguage);
+
 export default i18n;

src/pages/Dashboard.jsx

@@ -213,18 +213,18 @@ const Dashboard = () => {
                 } else if (profileResponse.status === 401) {
                     expireSession();
                 } else {
-                    setError(t('INFO.ERROR.LOAD_PROFILE'));
+                    setError('INFO.ERROR.LOAD_PROFILE');
                 }
             } catch (err) {
                 console.error('Dashboard fetch error:', err);
-                setError(t('INFO.ERROR.NETWORK_FAILURE'));
+                setError('INFO.ERROR.NETWORK_FAILURE');
             } finally {
                 setIsLoading(false);
             }
         };
 
         fetchUserData();
-    }, [navigate, expireSession, t, fetchSteamCount, fetchTopGames, fetchPlaying, fetchSummary, fetchActivity, fetchAchievements]);
+    }, [navigate, expireSession, fetchSteamCount, fetchTopGames, fetchPlaying, fetchSummary, fetchActivity, fetchAchievements]);
 
     const hasSteamId = !!userData?.steamId;
     const showLibrary = hasSteamId || steamData.count > 0;
@@ -248,7 +248,7 @@ const Dashboard = () => {
     if (error) {
         return (
             <div className="py-24 text-center text-destructive">
-                {error}
+                {t(error)}
             </div>
         );
     }

src/pages/GameDetail.jsx

@@ -89,6 +89,14 @@ export default function GameDetail() {
         shownLevel.current = {appid: data.appid, level: celebrationLevel(data)};
     }, [data]);
 
+    // Another game starts empty, already in this render. A reload of the same game keeps the old data, so the edit
+    // cards keep what is typed.
+    const [dataAppid, setDataAppid] = useState(appid);
+    if (dataAppid !== appid) {
+        setDataAppid(appid);
+        setData(null);
+    }
+
     useEffect(() => {
         let cancelled = false;
         if (!hasSession()) {
@@ -111,11 +119,11 @@ export default function GameDetail() {
                     return;
                 }
                 if (response.status === 404) {
-                    setError(t('GAME_DETAIL.NOT_FOUND'));
+                    setError('GAME_DETAIL.NOT_FOUND');
                     return;
                 }
                 if (!response.ok) {
-                    setError(t('GAME_DETAIL.ERROR_LOAD'));
+                    setError('GAME_DETAIL.ERROR_LOAD');
                     return;
                 }
                 const json = await response.json();
@@ -123,7 +131,7 @@ export default function GameDetail() {
             } catch (err) {
                 if (!cancelled) {
                     console.error('GameDetail load error:', err);
-                    setError(t('INFO.ERROR.NETWORK_FAILURE'));
+                    setError('INFO.ERROR.NETWORK_FAILURE');
                 }
             } finally {
                 if (!cancelled) setIsLoading(false);
@@ -132,7 +140,7 @@ export default function GameDetail() {
         return () => {
             cancelled = true;
         };
-    }, [appid, navigate, expireSession, t, reloads]);
+    }, [appid, navigate, expireSession, reloads]);
 
     const sortedAchievements = useMemo(() => {
         if (!data?.achievements) return [];
@@ -188,7 +196,7 @@ export default function GameDetail() {
                 <ArrowLeft/>{t('GAME_DETAIL.BACK')}
             </Button>
 
-            {isLoading && (
+            {isLoading && !data && (
                 <div className="space-y-6">
                     <Skeleton className="h-52 rounded-xl"/>
                     <Skeleton className="h-40 rounded-xl"/>
@@ -197,12 +205,12 @@ export default function GameDetail() {
 
             {error && !isLoading && (
                 <div className="py-12 text-center text-destructive space-y-4">
-                    <p>{error}</p>
+                    <p>{t(error)}</p>
                     <Button asChild variant="outline"><Link to="/library">{t('GAME_DETAIL.BACK_TO_LIBRARY')}</Link></Button>
                 </div>
             )}
 
-            {!isLoading && !error && data && (
+            {!error && data && (
                 <>
                     {data.hidden && (
                         <div role="status" className="flex items-center gap-2 rounded-lg border bg-muted/50 px-4 py-3 text-sm text-muted-foreground">

src/pages/GameDetail.reload.test.jsx

@@ -0,0 +1,44 @@
+// @vitest-environment jsdom
+import {afterEach, beforeEach, expect, it, vi} from 'vitest';
+import {cleanup, fireEvent, render, screen, waitFor} from '@testing-library/react';
+import {MemoryRouter, Route, Routes} from 'react-router-dom';
+import GameDetail from './GameDetail.jsx';
+import {PreferencesProvider} from '../context/PreferencesContext.jsx';
+
+vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
+// Stands in for a saved correction, which loads the game again.
+vi.mock('../components/GameCorrectionDialog.jsx', () => ({
+    default: ({onChanged}) => <button type="button" onClick={onChanged}>correction saved</button>,
+}));
+
+const game = {
+    appid: 220, name: 'Half-Life 2', playtimeMinutes: 100, playtime2Weeks: 90, status: 'BACKLOG',
+    rating: null, notes: null, priority: null, hasAchievements: false, statsVisible: false, achievements: [],
+};
+
+const gameLoads = () => fetch.mock.calls.filter(([url]) => url.endsWith('/api/library/games/220')).length;
+
+beforeEach(() => {
+    localStorage.setItem('tbp_session', '1');
+    globalThis.fetch = vi.fn(async (url) => ({ok: true, status: 200,
+        json: async () => (url.includes('/api/users/me') ? {role: 'AUDITOR', activeRole: 'AUDITOR'} : game)}));
+});
+
+afterEach(() => {
+    cleanup();
+    localStorage.clear();
+});
+
+it('keeps unsaved notes while the game loads again after a correction', async () => {
+    render(
+        <MemoryRouter initialEntries={['/library/220']}><PreferencesProvider>
+            <Routes><Route path="/library/:appid" element={<GameDetail/>}/></Routes>
+        </PreferencesProvider></MemoryRouter>,
+    );
+    fireEvent.change(await screen.findByLabelText('BACKLOG.NOTES_LABEL'), {target: {value: 'my draft'}});
+
+    fireEvent.click(await screen.findByRole('button', {name: 'correction saved'}));
+
+    await waitFor(() => expect(gameLoads()).toBe(2));
+    await waitFor(() => expect(screen.getByLabelText('BACKLOG.NOTES_LABEL').value).toBe('my draft'));
+});

src/pages/GameLibrary.jsx

@@ -89,7 +89,7 @@ export default function GameLibrary() {
             }
 
             if (!response.ok) {
-                setError(t('LIBRARY.ERROR_LOAD'));
+                setError('LIBRARY.ERROR_LOAD');
                 return;
             }
 
@@ -97,11 +97,11 @@ export default function GameLibrary() {
             setData(json);
         } catch (err) {
             console.error('Library load error:', err);
-            setError(t('INFO.ERROR.NETWORK_FAILURE'));
+            setError('INFO.ERROR.NETWORK_FAILURE');
         } finally {
             setIsLoading(false);
         }
-    }, [navigate, expireSession, page, size, sort, listStatus, q, listShortOnly, hiddenOnly, t]);
+    }, [navigate, expireSession, page, size, sort, listStatus, q, listShortOnly, hiddenOnly]);
 
     useEffect(() => {
         load();
@@ -287,7 +287,7 @@ export default function GameLibrary() {
                 </Card>
             )}
 
-            {error && <div className="py-12 text-center text-destructive">{error}</div>}
+            {error && <div className="py-12 text-center text-destructive">{t(error)}</div>}
 
             {ready && data.content.length === 0 && (
                 <Card className="items-center py-16 text-center text-muted-foreground">

src/pages/PublicProfilePage.jsx

@@ -51,11 +51,11 @@ export default function PublicProfilePage() {
                     `${import.meta.env.VITE_API_URL}/api/public/profiles/${encodeURIComponent(name)}`);
                 if (cancelled) return;
                 if (profileResponse.status === 404) {
-                    setError(t('PROFILE.NOT_FOUND'));
+                    setError('PROFILE.NOT_FOUND');
                     return;
                 }
                 if (!profileResponse.ok) {
-                    setError(t('PROFILE.ERROR_LOAD'));
+                    setError('PROFILE.ERROR_LOAD');
                     return;
                 }
                 const found = await profileResponse.json();
@@ -64,7 +64,7 @@ export default function PublicProfilePage() {
                 });
                 if (cancelled) return;
                 if (!libraryResponse.ok) {
-                    setError(t('PROFILE.ERROR_LOAD'));
+                    setError('PROFILE.ERROR_LOAD');
                     return;
                 }
                 const data = await libraryResponse.json();
@@ -74,20 +74,20 @@ export default function PublicProfilePage() {
                 }
             } catch (err) {
                 console.error('Public profile load error:', err);
-                if (!cancelled) setError(t('INFO.ERROR.NETWORK_FAILURE'));
+                if (!cancelled) setError('INFO.ERROR.NETWORK_FAILURE');
             }
         })();
         return () => {
             cancelled = true;
         };
-    }, [name, t, reloads]);
+    }, [name, reloads]);
 
     if (error) {
         return (
             <PageContainer className="p-4 md:p-8">
                 <Card className="items-center py-16 text-center text-muted-foreground">
                     <UserRoundX className="size-10"/>
-                    <p className="max-w-sm text-sm">{error}</p>
+                    <p className="max-w-sm text-sm">{t(error)}</p>
                     <Link to="/" className="text-sm font-medium text-primary hover:underline">{t('PROFILE.TO_START')}</Link>
                 </Card>
             </PageContainer>

src/pages/SettingsPage.jsx

@@ -31,6 +31,7 @@ import {coverUrl} from '../utils/games.js';
 import {apiFetch, refreshSession} from '../utils/api.js';
 import {hasSession, markSession} from '../utils/auth.js';
 import {FAVORITE_PLATFORMS, saveFavoritePlatform} from '../utils/platforms.js';
+import {LANGUAGES, saveSettings} from '../utils/settings.js';
 
 const BACKEND_ERROR_KEY = {
     DISPLAY_NAME_ALREADY_IN_USE: 'SETTINGS.ERROR_DISPLAY_NAME_IN_USE',
@@ -44,7 +45,6 @@ const STEAM_LINK_TOASTS = {
     failed: {show: toast.error, key: 'SETTINGS.STEAM_LINK.FAILED'},
 };
 
-const SUPPORTED_LANGUAGES = ['en', 'de'];
 // Radix Select has no empty value.
 const NO_FAVORITE = 'NONE';
 
@@ -81,7 +81,7 @@ export default function SettingsPage() {
         formState: {errors, isSubmitting},
     } = useForm({
         resolver: zodResolver(settingsSchema),
-        defaultValues: {useDarkTheme: true, language: 'en', displayName: ''},
+        defaultValues: {displayName: ''},
     });
 
     // A language change gives a new `t` and runs the effect again; the toast shows once.
@@ -123,42 +123,32 @@ export default function SettingsPage() {
                 }
 
                 if (!response.ok) {
-                    setLoadError(t('INFO.ERROR.LOAD_PROFILE'));
+                    setLoadError('INFO.ERROR.LOAD_PROFILE');
                     return;
                 }
 
                 const data = await response.json();
                 setProfile(data);
-                reset({
-                    useDarkTheme: !!data.settings?.useDarkTheme,
-                    language: data.settings?.language || 'en',
-                    displayName: data.displayName ?? '',
-                });
+                reset({displayName: data.displayName ?? ''});
             } catch (err) {
                 console.error('Settings load error:', err);
-                setLoadError(t('INFO.ERROR.NETWORK_FAILURE'));
+                setLoadError('INFO.ERROR.NETWORK_FAILURE');
             } finally {
                 setIsLoading(false);
             }
         };
 
         load();
-    }, [navigate, expireSession, reset, t, steamOutcome]);
+    }, [navigate, expireSession, reset, steamOutcome]);
 
-    const persistSettings = async (payload) => {
+    const persistSettings = async (send) => {
         if (!hasSession()) {
             navigate('/login');
             return {ok: false};
         }
 
         try {
-            const response = await apiFetch(`${import.meta.env.VITE_API_URL}/api/users/settings`, {
-                method: 'PUT',
-                headers: {
-                    'Content-Type': 'application/json',
-                },
-                body: JSON.stringify(payload),
-            });
+            const response = await send();
 
             if (response.status === 401) {
                 expireSession();
@@ -181,23 +171,14 @@ export default function SettingsPage() {
         }
     };
 
-    // The backend replaces all settings, so every save sends the saved values of the fields it does not change.
-    const savedSettings = () => ({
-        useDarkTheme: isDarkMode,
-        language: i18n.language,
-        displayName: profile?.displayName ?? null,
-        publicProfile: !!profile?.settings?.publicProfile,
-    });
-
     const handleDarkThemeToggle = async () => {
         const next = !isDarkMode;
         setDarkMode(next); // apply on the fly
-        await persistSettings({...savedSettings(), useDarkTheme: next});
+        await persistSettings(() => saveSettings({useDarkTheme: next}));
     };
 
     const handleLanguageChange = async (next) => {
-        setLanguage(next); // apply on the fly
-        await persistSettings({...savedSettings(), language: next});
+        await persistSettings(() => setLanguage(next));
     };
 
     const handleFavoritePlatformChange = async (value) => {
@@ -210,7 +191,7 @@ export default function SettingsPage() {
 
     const handlePublicProfileToggle = async () => {
         const next = !profile?.settings?.publicProfile;
-        const result = await persistSettings({...savedSettings(), publicProfile: next});
+        const result = await persistSettings(() => saveSettings({publicProfile: next}));
         if (result.ok) {
             setProfile((p) => ({...p, settings: {...p.settings, publicProfile: next}}));
         }
@@ -237,12 +218,8 @@ export default function SettingsPage() {
 
     const onSubmitProfile = async (values) => {
         // Without a name the profile has no link, so removing the name also makes it private.
-        const publicProfile = savedSettings().publicProfile && !!values.displayName;
-        const result = await persistSettings({
-            ...savedSettings(),
-            displayName: values.displayName,
-            publicProfile,
-        });
+        const publicProfile = !!profile?.settings?.publicProfile && !!values.displayName;
+        const result = await persistSettings(() => saveSettings({displayName: values.displayName, publicProfile}));
         if (result.ok) {
             setProfile((p) => (p ? {
                 ...p, displayName: values.displayName, settings: {...p.settings, publicProfile},
@@ -262,7 +239,7 @@ export default function SettingsPage() {
     }
 
     if (loadError) {
-        return <div className="py-24 text-center text-destructive">{loadError}</div>;
+        return <div className="py-24 text-center text-destructive">{t(loadError)}</div>;
     }
 
     const publicProfile = !!profile?.settings?.publicProfile;
@@ -313,7 +290,7 @@ export default function SettingsPage() {
                                 <SelectValue/>
                             </SelectTrigger>
                             <SelectContent>
-                                {SUPPORTED_LANGUAGES.map((lang) => (
+                                {LANGUAGES.map((lang) => (
                                     <SelectItem key={lang} value={lang}>
                                         {t(`SETTINGS.LANGUAGE_OPTIONS.${lang.toUpperCase()}`)}
                                     </SelectItem>

src/pages/SettingsPage.test.jsx

@@ -1,6 +1,6 @@
 // @vitest-environment jsdom
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
-import {cleanup, fireEvent, render, screen, waitFor, within} from '@testing-library/react';
+import {act, cleanup, fireEvent, render, screen, waitFor, within} from '@testing-library/react';
 import {MemoryRouter} from 'react-router-dom';
 import SettingsPage from './SettingsPage.jsx';
 import {PreferencesProvider} from '../context/PreferencesContext.jsx';
@@ -29,6 +29,24 @@ function renderPage(me) {
     render(<MemoryRouter><PreferencesProvider><SettingsPage/></PreferencesProvider></MemoryRouter>);
 }
 
+/**
+ * Auth with PUT /api/users/settings answered one by one through answer(); GET /api/users/me shows what was saved.
+ */
+function fakeAuth(me) {
+    const saved = structuredClone(me);
+    const open = [];
+    globalThis.fetch = vi.fn((url, init) => {
+        if (init?.method !== 'PUT') return Promise.resolve({ok: true, status: 200, json: async () => structuredClone(saved)});
+        return new Promise((resolve) => open.push(() => {
+            const body = JSON.parse(init.body);
+            saved.displayName = body.displayName;
+            Object.assign(saved.settings, {useDarkTheme: body.useDarkTheme, language: body.language, publicProfile: body.publicProfile});
+            resolve({ok: true, status: 204, json: async () => { throw new SyntaxError('no body'); }});
+        }));
+    });
+    return {answer: () => open.shift()()};
+}
+
 describe('SettingsPage public profile', () => {
     beforeEach(() => localStorage.setItem('tbp_session', '1'));
 
@@ -46,6 +64,20 @@ describe('SettingsPage public profile', () => {
         expect(puts()[0].publicProfile).toBe(true);
     });
 
+    it('builds a save on the one before it, also while that one is still open', async () => {
+        const auth = fakeAuth(profile());
+        render(<MemoryRouter><PreferencesProvider><SettingsPage/></PreferencesProvider></MemoryRouter>);
+
+        fireEvent.click(await screen.findByRole('switch', {name: 'SETTINGS.PUBLIC_PROFILE'}));
+        await waitFor(() => expect(puts()).toHaveLength(1));
+        fireEvent.click(screen.getByRole('switch', {name: 'SETTINGS.DARK_THEME'}));
+        await act(async () => auth.answer());
+
+        await waitFor(() => expect(puts()).toHaveLength(2));
+        expect(puts()[1]).toMatchObject({publicProfile: false, useDarkTheme: false, displayName: 'Lobo'});
+        await act(async () => auth.answer());
+    });
+
     it('turns the public profile off and shows the link while it is on', async () => {
         renderPage(profile());
 

src/pages/WishlistPage.jsx

@@ -40,20 +40,20 @@ export default function WishlistPage() {
                     return;
                 }
                 if (!response.ok) {
-                    setError(t('WISHLIST.ERROR_LOAD'));
+                    setError('WISHLIST.ERROR_LOAD');
                     return;
                 }
                 const json = await response.json();
                 if (!cancelled) setGames(json.games ?? []);
             } catch (err) {
                 console.error('Wishlist load error:', err);
-                if (!cancelled) setError(t('INFO.ERROR.NETWORK_FAILURE'));
+                if (!cancelled) setError('INFO.ERROR.NETWORK_FAILURE');
             }
         })();
         return () => {
             cancelled = true;
         };
-    }, [navigate, expireSession, t]);
+    }, [navigate, expireSession]);
 
     const shown = (games ?? []).filter((g) => !onlyOnSale || g.discountPct > 0);
     const onSaleCount = (games ?? []).filter((g) => g.discountPct > 0).length;
@@ -91,7 +91,7 @@ export default function WishlistPage() {
                 </Card>
             )}
 
-            {error && <div className="py-12 text-center text-destructive">{error}</div>}
+            {error && <div className="py-12 text-center text-destructive">{t(error)}</div>}
 
             {games !== null && shown.length === 0 && (
                 <Card className="items-center py-16 text-center text-muted-foreground">

src/pages/languageSwitch.test.jsx

@@ -0,0 +1,54 @@
+// @vitest-environment jsdom
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+import {cleanup, render, screen} from '@testing-library/react';
+import {MemoryRouter, Route, Routes} from 'react-router-dom';
+import {switchLanguage} from '../test/i18n-mock.js';
+import {PreferencesProvider} from '../context/PreferencesContext.jsx';
+import Dashboard from './Dashboard.jsx';
+import GameDetail from './GameDetail.jsx';
+import GameLibrary from './GameLibrary.jsx';
+import PublicProfilePage from './PublicProfilePage.jsx';
+import SettingsPage from './SettingsPage.jsx';
+import WishlistPage from './WishlistPage.jsx';
+
+vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
+
+const pages = [
+    ['Dashboard', '/', '/', <Dashboard/>, 'INFO.ERROR.LOAD_PROFILE'],
+    ['GameDetail', '/games/:appid', '/games/220', <GameDetail/>, 'GAME_DETAIL.ERROR_LOAD'],
+    ['GameLibrary', '/library', '/library', <GameLibrary/>, 'LIBRARY.ERROR_LOAD'],
+    ['PublicProfilePage', '/u/:name', '/u/Lobo', <PublicProfilePage/>, 'PROFILE.ERROR_LOAD'],
+    ['SettingsPage', '/settings', '/settings', <SettingsPage/>, 'INFO.ERROR.LOAD_PROFILE'],
+    ['WishlistPage', '/wishlist', '/wishlist', <WishlistPage/>, 'WISHLIST.ERROR_LOAD'],
+];
+
+beforeEach(() => {
+    localStorage.setItem('tbp_session', '1');
+    switchLanguage('de');
+    globalThis.fetch = vi.fn(async () => ({ok: false, status: 500, json: async () => ({})}));
+});
+
+afterEach(() => {
+    cleanup();
+    localStorage.clear();
+});
+
+describe('a language change', () => {
+    it.each(pages)('%s: loads nothing again and shows the error in the new language', async (name, path, url, page, errorKey) => {
+        const tree = () => (
+            <MemoryRouter initialEntries={[url]}>
+                <PreferencesProvider><Routes><Route path={path} element={page}/></Routes></PreferencesProvider>
+            </MemoryRouter>
+        );
+        const {rerender} = render(tree());
+        await screen.findByText(`de:${errorKey}`);
+        const requests = fetch.mock.calls.length;
+
+        switchLanguage('en');
+        rerender(tree());
+
+        expect(await screen.findByText(`en:${errorKey}`)).toBeTruthy();
+        await new Promise((resolve) => setTimeout(resolve, 50));
+        expect(fetch.mock.calls.length).toBe(requests);
+    });
+});

src/test/i18n-mock.js

@@ -1,6 +1,15 @@
 // Module mock for react-i18next: t() returns the key (plus ":<count>" for plurals), so tests do not depend on the texts.
 // Use in a test file: vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
-const t = (key, options) => (options?.count === undefined ? key : `${key}:${options.count}`);
-const i18n = {language: 'de'};
+const translate = (key, options) => (options?.count === undefined ? key : `${key}:${options.count}`);
+let t = translate;
+const i18n = {language: 'de', changeLanguage: (language) => { i18n.language = language; }};
 
 export const useTranslation = () => ({t, i18n});
+
+/**
+ * A new `t` that puts `language:` before each key, like react-i18next gives a new `t` on a language change. Rerender
+ * to see it.
+ */
+export const switchLanguage = (language) => {
+    t = (key, options) => `${language}:${translate(key, options)}`;
+};

src/utils/appearance.js

@@ -1,4 +1,5 @@
 import {apiFetch} from './api.js';
+import {fetchMe, REQUEST_TIMEOUT_MS} from './settings.js';
 
 // Auth accepts only these names (AppearanceRequest); style.css has a preset for each.
 export const ACCENTS = ['violet', 'blue', 'green', 'orange', 'pink', 'red'];
@@ -12,7 +13,6 @@ export const DEFAULT_APPEARANCE = {
 export const appid = (value) => (Number.isInteger(value) && value > 0 ? value : null);
 
 const STORAGE_KEY = 'tbp_appearance';
-const REQUEST_TIMEOUT_MS = 10000;
 
 export const normalizeAppearance = (value) => ({
     accent: ACCENTS.includes(value?.accent) ? value.accent : DEFAULT_APPEARANCE.accent,
@@ -60,14 +60,16 @@ export const saveAppearance = (appearance) =>
     });
 
 /**
- * GET /api/users/me on Auth, only for its appearance. Null when there is no answer to use.
+ * GET /api/users/me on Auth, for its appearance (null when none is saved) and its language ('' when none is chosen).
+ * Null when there is no answer to use.
  */
-export const loadAppearance = async () => {
-    const response = await apiFetch(`${import.meta.env.VITE_API_URL}/api/users/me?v=1`, {
-        // Saves wait for this load.
-        signal: AbortSignal.timeout(REQUEST_TIMEOUT_MS),
-    });
+export const loadPreferences = async () => {
+    // Saves wait for this load, so it has a timeout.
+    const response = await fetchMe();
     if (!response.ok) return null;
     const data = await response.json();
-    return data.settings?.appearance ? normalizeAppearance(data.settings.appearance) : null;
+    return {
+        appearance: data.settings?.appearance ? normalizeAppearance(data.settings.appearance) : null,
+        language: data.settings?.language ?? '',
+    };
 };

src/utils/settings.js

@@ -0,0 +1,60 @@
+import {apiFetch} from './api.js';
+
+export const LANGUAGES = ['en', 'de'];
+
+const LANGUAGE_STORAGE_KEY = 'tbp_language';
+export const REQUEST_TIMEOUT_MS = 10000;
+
+export const readCachedLanguage = () => {
+    try {
+        const stored = localStorage.getItem(LANGUAGE_STORAGE_KEY);
+        return LANGUAGES.includes(stored) ? stored : null;
+    } catch {
+        return null;
+    }
+};
+
+export const cacheLanguage = (language) => {
+    try {
+        localStorage.setItem(LANGUAGE_STORAGE_KEY, language);
+    } catch {
+        // Private mode or a full storage: the language is only not cached.
+    }
+};
+
+/**
+ * GET /api/users/me on Auth. The caller handles the response status.
+ */
+export const fetchMe = () => apiFetch(`${import.meta.env.VITE_API_URL}/api/users/me?v=1`, {
+    signal: AbortSignal.timeout(REQUEST_TIMEOUT_MS),
+});
+
+let queue = Promise.resolve();
+
+/**
+ * PUT /api/users/settings on Auth with `changes`. That endpoint replaces all four fields, so each save first loads
+ * the saved ones; saves run one after another, from every page. The caller handles the response status.
+ */
+export const saveSettings = (changes) => {
+    const save = async () => {
+        const me = await fetchMe();
+        if (!me.ok) return me;
+        const data = await me.json();
+        return apiFetch(`${import.meta.env.VITE_API_URL}/api/users/settings`, {
+            method: 'PUT',
+            headers: {'Content-Type': 'application/json'},
+            body: JSON.stringify({
+                useDarkTheme: !!data.settings?.useDarkTheme,
+                language: data.settings?.language ?? '',
+                displayName: data.displayName ?? null,
+                publicProfile: !!data.settings?.publicProfile,
+                ...changes,
+            }),
+            // A hung request must not hold back the next saves.
+            signal: AbortSignal.timeout(REQUEST_TIMEOUT_MS),
+        });
+    };
+    const result = queue.then(save, save);
+    queue = result.catch(() => {});
+    return result;
+};

src/utils/settings.test.js

@@ -0,0 +1,15 @@
+// @vitest-environment jsdom
+import {afterEach, describe, expect, it} from 'vitest';
+import {cacheLanguage, readCachedLanguage} from './settings.js';
+
+afterEach(() => localStorage.clear());
+
+describe('language cache', () => {
+    it('gives back the cached language, and nothing for an unknown one', () => {
+        expect(readCachedLanguage()).toBeNull();
+        cacheLanguage('en');
+        expect(readCachedLanguage()).toBe('en');
+        localStorage.setItem('tbp_language', 'fr');
+        expect(readCachedLanguage()).toBeNull();
+    });
+});

src/utils/validation.js

@@ -7,9 +7,11 @@ const emailField = z
     .min(1, 'VALIDATION.EMAIL_REQUIRED')
     .email('VALIDATION.EMAIL_INVALID');
 
+// Auth hashes with BCrypt, which takes at most 72 bytes.
 const passwordField = z
     .string()
-    .min(8, 'VALIDATION.PASSWORD_TOO_SHORT');
+    .min(8, 'VALIDATION.PASSWORD_TOO_SHORT')
+    .refine((value) => new TextEncoder().encode(value).length <= 72, 'VALIDATION.PASSWORD_TOO_LONG');
 
 const inviteCodeField = z
     .string()
@@ -40,7 +42,5 @@ export const registrationSchema = z
     });
 
 export const settingsSchema = z.object({
-    useDarkTheme: z.boolean(),
-    language: z.enum(['en', 'de'], {message: 'VALIDATION.LANGUAGE_INVALID'}),
     displayName: displayNameField,
 });

src/utils/validation.test.js

@@ -29,3 +29,12 @@ describe('displayName validation', () => {
     });
 });
 
+
+describe('registration password', () => {
+    it('rejects a password over 72 UTF-8 bytes, as Auth does', () => {
+        const password = 'é'.repeat(37);
+        expect(registrationSchema.safeParse({
+            email: 'a@b.de', password, passwordConfirmation: password, inviteCode: 'code',
+        }).success).toBe(false);
+    });
+});