diff --git a/apps/stage-tamagotchi/src/main/configs/global.ts b/apps/stage-tamagotchi/src/main/configs/global.ts
index 211307bda..88477d414 100644
--- a/apps/stage-tamagotchi/src/main/configs/global.ts
+++ b/apps/stage-tamagotchi/src/main/configs/global.ts
@@ -3,7 +3,7 @@ import { object, optional, picklist, string } from 'valibot'
 import { createConfig } from '../libs/electron/persistence'
 
 export const globalAppConfigSchema = object({
-  language: optional(string(), 'en'),
+  language: optional(string()),
   updateChannel: optional(picklist(['latest', 'stable', 'alpha', 'beta', 'nightly', 'canary'])),
 })
 
diff --git a/apps/stage-tamagotchi/src/main/services/airi/i18n/index.ts b/apps/stage-tamagotchi/src/main/services/airi/i18n/index.ts
index 303e08af6..e98df79c8 100644
--- a/apps/stage-tamagotchi/src/main/services/airi/i18n/index.ts
+++ b/apps/stage-tamagotchi/src/main/services/airi/i18n/index.ts
@@ -1,4 +1,3 @@
-import type { LocaleDetector } from '@intlify/core'
 import type { createContext } from '@moeru/eventa/adapters/electron/main'
 import type { BrowserWindow } from 'electron'
 import type { ProvidedBy } from 'injeca'
@@ -18,14 +17,11 @@ export async function createI18nService(params: { context: ReturnType<typeof cre
 
   defineInvokeHandler(params.context, i18nSetLocale, (locale) => {
     const current = config.get()
-    if (current) {
-      config.update({ ...current, language: locale as string })
-    }
+    config.update({ ...current, language: locale as string })
     params.i18n.locale(locale)
   })
 
   defineInvokeHandler(params.context, i18nGetLocale, () => {
-    const locale = params.i18n.locale as () => string | LocaleDetector<any[]> | undefined
-    return locale()
+    return config.get()?.language
   })
 }
diff --git a/apps/stage-tamagotchi/src/renderer/App.vue b/apps/stage-tamagotchi/src/renderer/App.vue
index 754c9c6a0..cc51f7841 100644
--- a/apps/stage-tamagotchi/src/renderer/App.vue
+++ b/apps/stage-tamagotchi/src/renderer/App.vue
@@ -20,7 +20,6 @@ import { useSettings, useSettingsAudioDevice } from '@proj-airi/stage-ui/stores/
 import { useTheme } from '@proj-airi/ui'
 import { storeToRefs } from 'pinia'
 import { onMounted, onUnmounted, watch } from 'vue'
-import { useI18n } from 'vue-i18n'
 import { RouterView, useRoute, useRouter } from 'vue-router'
 import { toast, Toaster } from 'vue-sonner'
 
@@ -32,6 +31,7 @@ import {
   electronGodotStageStatusChanged,
   electronSettingsNavigate,
   electronStartTrackMousePosition,
+  i18nGetLocale,
   i18nSetLocale,
 } from '../shared/eventa'
 import {
@@ -50,13 +50,13 @@ import {
 } from '../shared/eventa/plugin/host'
 import { initializeElectronAuthCallbackBridge } from './bridges/electron-auth-callback'
 import { initializeStageThreeRuntimeTraceBridge } from './bridges/stage-three-runtime-trace'
+import { useLanguage } from './composables/use-language'
 import { useTamagotchiMcpToolsStore } from './stores/mcp-tools'
 import { useTamagotchiPluginToolsStore } from './stores/plugin-tools'
 import { useServerChannelSettingsStore } from './stores/settings/server-channel'
 import { useStageWindowLifecycleStore } from './stores/stage-window-lifecycle'
 
 const { isDark: dark } = useTheme()
-const i18n = useI18n()
 const contextBridgeStore = useContextBridgeStore()
 const displayModelsStore = useDisplayModelsStore()
 const settingsStore = useSettings()
@@ -92,6 +92,7 @@ const unloadPlugin = useElectronEventaInvoke(electronPluginUnload)
 const inspectPluginHost = useElectronEventaInvoke(electronPluginInspect)
 const startTrackingCursorPoint = useElectronEventaInvoke(electronStartTrackMousePosition)
 const reportPluginCapability = useElectronEventaInvoke(electronPluginUpdateCapability)
+const getMainLocale = useElectronEventaInvoke(i18nGetLocale)
 const setLocale = useElectronEventaInvoke(i18nSetLocale)
 const getGodotStageStatus = useElectronEventaInvoke(electronGodotStageGetStatus)
 const syncArtistryConfig = useElectronEventaInvoke(artistrySyncConfig)
@@ -156,10 +157,7 @@ void mcpToolsStore.refresh().catch((error) => {
 })
 void refreshPluginRuntimeTools()
 
-watch(language, () => {
-  i18n.locale.value = language.value || 'en'
-  setLocale(language.value || 'en')
-})
+const { restore: restoreLocale } = useLanguage(language, getMainLocale, setLocale)
 
 watch([activeProvider, artistryGlobals, activeModel, defaultPromptPrefix, providerOptions], () => {
   if (activeProvider.value) {
@@ -198,6 +196,14 @@ context.value.on(electronGodotStageStatusChanged, (event) => {
 })
 
 onMounted(async () => {
+  // NOTICE: Issue #1658
+  // When Electron restarts, renderer localStorage may not be flushed to disk.
+  // The store's onMounted hook falls back to navigator.language, which triggers
+  // watch(language) and overwrites the main-process config with the OS locale.
+  // We must restore the correct locale from main process before allowing sync.
+  // https://github.com/moeru-ai/airi/issues/1658
+  await restoreLocale()
+
   analyticsStore.initialize()
   await displayModelsStore.initialize()
   cardStore.initialize()
diff --git a/apps/stage-tamagotchi/src/renderer/composables/use-language.test.ts b/apps/stage-tamagotchi/src/renderer/composables/use-language.test.ts
new file mode 100644
index 000000000..2d30094cd
--- /dev/null
+++ b/apps/stage-tamagotchi/src/renderer/composables/use-language.test.ts
@@ -0,0 +1,166 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { nextTick, ref } from 'vue'
+
+import { useLanguage } from './use-language'
+
+vi.mock('vue-i18n', () => ({
+  useI18n: () => ({
+    locale: { value: 'en' },
+  }),
+}))
+
+const localStorageMock = (() => {
+  let store: Record<string, string> = {}
+  return {
+    getItem: (key: string) => store[key] ?? null,
+    setItem: (key: string, value: string) => { store[key] = value },
+    removeItem: (key: string) => { delete store[key] },
+    clear: () => { store = {} },
+  }
+})()
+
+Object.defineProperty(globalThis, 'localStorage', { value: localStorageMock })
+
+vi.mock('@proj-airi/stage-shared/composables', () => ({
+  useLocalStorageManualReset: vi.fn((key: string, initialValue: string) => {
+    // Tests control persisted state by pre-seeding localStorage before each case
+    const stored = localStorageMock.getItem(key)
+    const value = stored !== null ? stored : initialValue
+    return ref(value)
+  }),
+}))
+
+describe('useLanguage', () => {
+  beforeEach(() => {
+    vi.restoreAllMocks()
+    localStorageMock.clear()
+  })
+
+  // ROOT CAUSE:
+  // https://github.com/moeru-ai/airi/issues/1658
+  // When Electron restarts, renderer localStorage may not be flushed.
+  // The store's onMounted hook falls back to navigator.language, then
+  // watch(language) propagates that wrong locale back to main config.
+  // useLanguage prevents this by guarding sync until the correct
+  // locale is restored from the main-process config.
+  it('issue #1658: restores correct locale from main process when store fallback is wrong', async () => {
+    const language = ref('zh-Hans') // simulate store fallback to OS locale
+    const getMainLocale = vi.fn(async () => 'zh-Hant') // main has user selection
+    const setLocale = vi.fn(async () => {})
+
+    // No persisted language in localStorage → renderer lost its setting
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    expect(getMainLocale).toHaveBeenCalledTimes(1)
+    expect(language.value).toBe('zh-Hant')
+    expect(setLocale).toHaveBeenCalledWith('zh-Hant')
+  })
+
+  it('issue #1658: does not change language when main locale matches store', async () => {
+    const language = ref('zh-Hant')
+    const getMainLocale = vi.fn(async () => 'zh-Hant')
+    const setLocale = vi.fn(async () => {})
+
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    expect(language.value).toBe('zh-Hant')
+    expect(setLocale).toHaveBeenCalledWith('zh-Hant')
+  })
+
+  it('does not overwrite valid renderer locale when persisted language exists', async () => {
+    localStorage.setItem('settings/language', 'ja')
+
+    const language = ref('ja') // user explicitly set this before
+    const getMainLocale = vi.fn(async () => 'en')
+    const setLocale = vi.fn(async () => {})
+
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    // Should NOT call getMainLocale because renderer has persisted value
+    expect(getMainLocale).not.toHaveBeenCalled()
+    expect(language.value).toBe('ja')
+    expect(setLocale).toHaveBeenCalledWith('ja')
+  })
+
+  it('preserves OS locale on first launch when main has no saved language', async () => {
+    const language = ref('zh-Hans') // OS-detected fallback
+    const getMainLocale = vi.fn(async () => undefined) // no config file yet
+    const setLocale = vi.fn(async () => {})
+
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    expect(getMainLocale).toHaveBeenCalledTimes(1)
+    expect(language.value).toBe('zh-Hans') // keep OS fallback
+    expect(setLocale).toHaveBeenCalledWith('zh-Hans')
+  })
+
+  it('restores explicit English choice after localStorage loss', async () => {
+    const language = ref('zh-Hans') // store fallback to OS locale
+    const getMainLocale = vi.fn(async () => 'en') // user explicitly chose English
+    const setLocale = vi.fn(async () => {})
+
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    expect(getMainLocale).toHaveBeenCalledTimes(1)
+    expect(language.value).toBe('en')
+    expect(setLocale).toHaveBeenCalledWith('en')
+  })
+
+  it('continues startup when getMainLocale fails', async () => {
+    const consoleSpy = vi.spyOn(console, 'warn').mockImplementation(() => {})
+    const language = ref('zh-Hans')
+    const getMainLocale = vi.fn(async () => {
+      throw new Error('IPC timeout')
+    })
+    const setLocale = vi.fn(async () => {})
+
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    // Should not throw; should still enable sync and use current value
+    expect(language.value).toBe('zh-Hans')
+    expect(setLocale).toHaveBeenCalledWith('zh-Hans')
+    expect(consoleSpy).toHaveBeenCalledWith(
+      '[useLanguage] Failed to get locale from main process, using fallback:',
+      expect.any(Error),
+    )
+
+    consoleSpy.mockRestore()
+  })
+
+  it('does not sync to main before restore is called', () => {
+    const language = ref('en')
+    const getMainLocale = vi.fn(async () => 'en')
+    const setLocale = vi.fn(async () => {})
+
+    useLanguage(language, getMainLocale, setLocale)
+
+    // Simulate the store's onMounted fallback changing language
+    language.value = 'zh-Hans'
+
+    expect(setLocale).not.toHaveBeenCalled()
+  })
+
+  it('syncs to main after restore is called', async () => {
+    const language = ref('en')
+    const getMainLocale = vi.fn(async () => 'en')
+    const setLocale = vi.fn(async () => {})
+
+    const { restore } = useLanguage(language, getMainLocale, setLocale)
+    await restore()
+
+    // Clear the restore() call so we only assert the post-restore sync
+    setLocale.mockClear()
+
+    // Now changes should propagate
+    language.value = 'ja'
+    await nextTick()
+
+    expect(setLocale).toHaveBeenCalledWith('ja')
+  })
+})
diff --git a/apps/stage-tamagotchi/src/renderer/composables/use-language.ts b/apps/stage-tamagotchi/src/renderer/composables/use-language.ts
new file mode 100644
index 000000000..c56a3ef94
--- /dev/null
+++ b/apps/stage-tamagotchi/src/renderer/composables/use-language.ts
@@ -0,0 +1,63 @@
+import type { Ref } from 'vue'
+
+import { useLocalStorageManualReset } from '@proj-airi/stage-shared/composables'
+import { watch } from 'vue'
+import { useI18n } from 'vue-i18n'
+
+/**
+ * Manages language sync between renderer and main process, guarding
+ * against Electron localStorage flush issues on restart.
+ *
+ * Use when:
+ * - Electron restarts and renderer localStorage may not have been flushed
+ *
+ * Expects:
+ * - `language` is the reactive language ref from the settings store
+ * - `getMainLocale` returns the raw locale persisted in main-process config
+ *   (`undefined` when no config exists yet, a string when user saved one)
+ * - `setLocale` syncs the renderer locale back to main process
+ *
+ * Returns:
+ * - `restore()` to be called during component onMounted
+ */
+export function useLanguage(
+  language: Ref<string>,
+  getMainLocale: () => Promise<unknown>,
+  setLocale: (locale: string) => Promise<unknown> | unknown,
+) {
+  const i18n = useI18n()
+  const persistedLanguage = useLocalStorageManualReset<string>('settings/language', '')
+  const hasPersistedLanguage = persistedLanguage.value !== ''
+  let isLocaleSynced = false
+
+  // Guard: do not propagate the store's navigator.language fallback back
+  // to main-process config before we have verified the correct locale.
+  watch(language, () => {
+    i18n.locale.value = language.value || 'en'
+    if (isLocaleSynced) {
+      void setLocale(language.value || 'en')
+    }
+  })
+
+  async function restore() {
+    // Only trust main-process locale when renderer has lost its own setting.
+    // When main returns undefined, no language has ever been explicitly saved
+    // (true first launch), so we keep the renderer's OS-detected fallback.
+    // When main returns a string, that is the user's explicit choice.
+    if (!hasPersistedLanguage) {
+      try {
+        const mainLocale = await getMainLocale()
+        if (typeof mainLocale === 'string' && mainLocale && mainLocale !== language.value) {
+          language.value = mainLocale
+        }
+      }
+      catch (error) {
+        console.warn('[useLanguage] Failed to get locale from main process, using fallback:', error)
+      }
+    }
+    isLocaleSynced = true
+    void setLocale(language.value || 'en')
+  }
+
+  return { restore }
+}
diff --git a/apps/stage-tamagotchi/src/shared/eventa/index.ts b/apps/stage-tamagotchi/src/shared/eventa/index.ts
index 3c07b3ee4..b99a5accd 100644
--- a/apps/stage-tamagotchi/src/shared/eventa/index.ts
+++ b/apps/stage-tamagotchi/src/shared/eventa/index.ts
@@ -414,7 +414,7 @@ export const electronAuthCallbackError = defineEventa<{ error: string }>('eventa
 export const electronAuthLogout = defineInvokeEventa<void>('eventa:invoke:electron:auth:logout')
 
 export const i18nSetLocale = defineInvokeEventa<void, Locale>('eventa:invoke:electron:i18n:set-locale')
-export const i18nGetLocale = defineInvokeEventa<Locale>('eventa:invoke:electron:i18n:get-locale')
+export const i18nGetLocale = defineInvokeEventa<string | undefined>('eventa:invoke:electron:i18n:get-locale')
 
 export { electron } from '@proj-airi/electron-eventa'
 export * from '@proj-airi/electron-eventa/electron-updater'
diff --git a/packages/stage-ui/src/stores/settings/general.test.ts b/packages/stage-ui/src/stores/settings/general.test.ts
new file mode 100644
index 000000000..eca515879
--- /dev/null
+++ b/packages/stage-ui/src/stores/settings/general.test.ts
@@ -0,0 +1,67 @@
+import { createTestingPinia } from '@pinia/testing'
+import { setActivePinia } from 'pinia'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { useSettingsGeneral } from './general'
+
+vi.mock('vue-i18n', () => ({
+  useI18n: () => ({
+    t: (key: string) => key,
+  }),
+}))
+
+describe('store settings-general', () => {
+  let store: Record<string, string>
+  let localStorageMock: Storage
+
+  beforeEach(() => {
+    const pinia = createTestingPinia({ createSpy: vi.fn, stubActions: false })
+    setActivePinia(pinia)
+
+    store = {}
+    localStorageMock = {
+      getItem: vi.fn((key: string) => store[key] ?? null),
+      setItem: vi.fn((key: string, value: string) => { store[key] = value }),
+      removeItem: vi.fn((key: string) => { delete store[key] }),
+      clear: vi.fn(() => { for (const key in store) delete store[key] }),
+      length: 0,
+      key: vi.fn(() => null),
+    } as unknown as Storage
+
+    vi.stubGlobal('localStorage', localStorageMock)
+  })
+
+  afterEach(() => {
+    vi.unstubAllGlobals()
+  })
+
+  // ROOT CAUSE:
+  // https://github.com/moeru-ai/airi/issues/1658
+  // When Electron client is fully restarted, renderer localStorage may not be
+  // flushed to disk. On next startup, getLanguage() finds no persisted value
+  // and falls back to navigator.language (OS locale), ignoring the user's
+  // previous selection.
+  it('issue #1658: falls back to navigator.language when localStorage is empty', () => {
+    // Simulate Electron restart where localStorage for language is lost
+    vi.stubGlobal('navigator', { language: 'zh-CN' })
+
+    const settingsStore = useSettingsGeneral()
+    const resolvedLanguage = settingsStore.getLanguage()
+
+    // navigator.language 'zh-CN' gets remapped to 'zh-Hans'
+    expect(resolvedLanguage).toBe('zh-Hans')
+    expect(localStorageMock.getItem).toHaveBeenCalledWith('settings/language')
+  })
+
+  it('issue #1658: returns persisted language when localStorage has a value', () => {
+    // User previously selected Traditional Chinese
+    store['settings/language'] = 'zh-Hant'
+    vi.stubGlobal('navigator', { language: 'zh-CN' })
+
+    const settingsStore = useSettingsGeneral()
+    const resolvedLanguage = settingsStore.getLanguage()
+
+    // Should respect the persisted language, not fallback to navigator.language
+    expect(resolvedLanguage).toBe('zh-Hant')
+  })
+})