diff --git a/app.vue b/app.vue
index 112f8ef..9da0a7f 100644
--- a/app.vue
+++ b/app.vue
@@ -6,6 +6,7 @@
 
 <script setup lang="ts">
 import { invoke } from '@tauri-apps/api/core'
+import { useLocale } from '~/composables/useLocale'
 import { useWallet } from '~/composables/useWallet'
 import { useTheme } from '~/composables/useTheme'
 import { useSettingsStore } from '~/stores/settings'
@@ -31,8 +32,14 @@ const nodesStore = useNodesStore()
 const filesStore = useFilesStore()
 const connectionStore = useConnectionStore()
 
+const { init: initLocale } = useLocale()
+
 onMounted(async () => {
+  // Config first — useLocale.init() reads the persisted choice from
+  // settingsStore.i18nLocale, so the store must be hydrated before we resolve.
   await settingsStore.loadConfig()
+  await initLocale()
+
   await settingsStore.loadDevnetManifest()
   nodesStore.init()
   filesStore.loadHistory()
diff --git a/components/AppHeader.vue b/components/AppHeader.vue
index 0014612..bbe0dee 100644
--- a/components/AppHeader.vue
+++ b/components/AppHeader.vue
@@ -1,7 +1,7 @@
 <template>
   <header class="flex h-12 items-center justify-between border-b border-autonomi-border bg-autonomi-surface px-4">
     <!-- Page title -->
-    <h1 class="text-sm font-medium text-autonomi-text">{{ pageTitle }}</h1>
+    <h1 class="text-sm font-medium text-autonomi-text">{{ $t(pageTitleKey) }}</h1>
 
     <!-- Right side: status indicators + wallet -->
     <div class="flex items-center gap-4">
@@ -9,7 +9,7 @@
       <div v-if="filesStore.hasActiveTransfers" class="flex items-center gap-2 text-xs">
         <span class="text-autonomi-blue">↑↓</span>
         <span class="text-autonomi-muted">
-          {{ filesStore.pinnedFiles.length }} active
+          {{ $t('header.active_transfers', { count: filesStore.pinnedFiles.length }) }}
         </span>
       </div>
 
@@ -17,27 +17,27 @@
       <div
         v-if="connectionStore.isConnecting"
         class="flex items-center gap-2 rounded-md border border-autonomi-border px-2.5 py-1 text-xs text-autonomi-muted"
-        title="Connecting to the Autonomi network"
+        :title="$t('header.connecting_tooltip')"
       >
         <div class="h-2.5 w-2.5 animate-spin rounded-full border-2 border-yellow-500 border-t-transparent" />
-        <span>Connecting</span>
+        <span>{{ $t('header.connecting') }}</span>
       </div>
       <div
         v-else-if="connectionStore.isConnected"
         class="flex items-center gap-2 rounded-md border border-autonomi-border px-2.5 py-1 text-xs text-autonomi-text"
-        title="Connected to the Autonomi network"
+        :title="$t('header.connected_tooltip')"
       >
         <span class="text-autonomi-success">●</span>
-        <span>Network</span>
+        <span>{{ $t('header.connected') }}</span>
       </div>
       <button
         v-else-if="connectionStore.hasFailed"
         class="flex items-center gap-2 rounded-md border border-red-500/30 bg-red-500/5 px-2.5 py-1 text-xs text-red-400 hover:bg-red-500/10"
-        title="Connection failed — click to retry"
+        :title="$t('header.offline_tooltip')"
         @click="connectionStore.retry()"
       >
         <span>●</span>
-        <span>Offline · Retry</span>
+        <span>{{ $t('header.offline') }}</span>
       </button>
 
       <!-- Indelible indicator (replaces wallet when connected) -->
@@ -64,7 +64,7 @@
           class="rounded-md bg-autonomi-blue px-2.5 py-1 text-xs font-medium text-white hover:opacity-90"
           @click="openModal"
         >
-          Connect Wallet
+          {{ $t('header.connect_wallet') }}
         </button>
       </template>
     </div>
@@ -98,14 +98,14 @@ function openModal() {
   }
 }
 
-const pageTitle = computed(() => {
-  const titles: Record<string, string> = {
-    '/': 'Nodes',
-    '/files': 'Files',
-    '/wallet': 'Wallet',
-    '/settings': 'Settings',
+const pageTitleKey = computed(() => {
+  const keys: Record<string, string> = {
+    '/': 'nav.nodes',
+    '/files': 'nav.files',
+    '/wallet': 'nav.wallet',
+    '/settings': 'nav.settings',
   }
-  return titles[route.path] ?? 'Autonomi'
+  return keys[route.path] ?? 'header.title'
 })
 
 </script>
diff --git a/components/AppSidebar.vue b/components/AppSidebar.vue
index 2262923..d06cb41 100644
--- a/components/AppSidebar.vue
+++ b/components/AppSidebar.vue
@@ -17,15 +17,15 @@
         v-if="isPrereleaseBuild"
         class="mb-2 rounded-md bg-teal-500/10 border border-teal-500/20 px-3 py-1.5 text-center text-xs font-medium text-teal-400"
       >
-        PRE-RELEASE
+        {{ $t('sidebar.pre_release') }}
       </div>
 
       <!-- Network mode indicator -->
       <div
-        v-if="settingsStore.devnetActive && networkLabel"
+        v-if="settingsStore.devnetActive && networkLabelKey"
         class="mb-2 rounded-md bg-amber-500/10 border border-amber-500/20 px-3 py-1.5 text-center text-xs font-medium text-amber-400"
       >
-        {{ networkLabel }}
+        {{ $t(networkLabelKey) }}
       </div>
 
       <!-- Update banner -->
@@ -42,9 +42,9 @@
             v-if="updaterStore.isPrerelease"
             class="text-[10px] font-bold uppercase tracking-wider opacity-70"
           >
-            Pre-Release
+            {{ $t('sidebar.update_pre_release_tag') }}
           </div>
-          <div class="text-xs font-bold uppercase tracking-wide">Update Available</div>
+          <div class="text-xs font-bold uppercase tracking-wide">{{ $t('sidebar.update_available') }}</div>
           <div class="truncate text-xs font-medium opacity-80">v{{ updaterStore.version }}</div>
         </div>
         <span v-if="updaterStore.installing" class="h-4 w-4 animate-spin rounded-full border-2 border-gray-900/30 border-t-gray-900" />
@@ -60,7 +60,7 @@
           : 'text-autonomi-muted hover:bg-autonomi-border/50 hover:text-autonomi-text'"
       >
         <span class="text-base">{{ item.icon }}</span>
-        <span>{{ item.label }}</span>
+        <span>{{ $t(item.labelKey) }}</span>
       </NuxtLink>
     </nav>
 
@@ -74,7 +74,7 @@
           : 'text-autonomi-muted hover:bg-autonomi-border/50 hover:text-autonomi-text'"
       >
         <span class="text-base">⚙</span>
-        <span>Settings</span>
+        <span>{{ $t('nav.settings') }}</span>
       </NuxtLink>
     </div>
   </aside>
@@ -109,18 +109,18 @@ const isPrereleaseBuild = computed(() =>
   /-(?:rc|beta|alpha)\./.test(currentVersion.value ?? ''),
 )
 
-const networkLabel = computed<string | null>(() => {
+const networkLabelKey = computed<string | null>(() => {
   switch (settingsStore.devnetChainId) {
-    case arbitrumSepolia.id: return 'SEPOLIA TESTNET'
-    case ANVIL_CHAIN_ID: return 'DEVNET'
+    case arbitrumSepolia.id: return 'sidebar.network_sepolia'
+    case ANVIL_CHAIN_ID: return 'sidebar.network_devnet'
     default: return null  // mainnet or unset — no badge
   }
 })
 
 const mainNav = computed(() => [
-  { path: '/', label: 'Nodes', icon: '⬡' },
-  { path: '/files', label: 'Files', icon: '◫' },
-  { path: '/wallet', label: 'Wallet', icon: '◎' },
+  { path: '/', labelKey: 'nav.nodes', icon: '⬡' },
+  { path: '/files', labelKey: 'nav.files', icon: '◫' },
+  { path: '/wallet', labelKey: 'nav.wallet', icon: '◎' },
 ])
 
 function isActive(path: string) {
diff --git a/composables/useLocale.ts b/composables/useLocale.ts
new file mode 100644
index 0000000..95e8889
--- /dev/null
+++ b/composables/useLocale.ts
@@ -0,0 +1,80 @@
+import { ref } from 'vue'
+import { locale as osLocaleApi } from '@tauri-apps/plugin-os'
+import { useI18n } from 'vue-i18n'
+import { useSettingsStore } from '~/stores/settings'
+
+export const SUPPORTED_LOCALES = ['en', 'ja'] as const
+export type SupportedLocale = typeof SUPPORTED_LOCALES[number]
+const DEFAULT_LOCALE: SupportedLocale = 'en'
+
+/** Each locale's name in its own script. Used in the Settings picker so the
+ *  user sees "English" / "日本語" regardless of the currently-active UI locale. */
+export const NATIVE_LOCALE_NAMES: Record<SupportedLocale, string> = {
+  en: 'English',
+  ja: '日本語',
+}
+
+/** Module-scoped cache of the OS-resolved locale. Warmed on the first
+ *  detectOsLocale() call so the Settings picker can render
+ *  "System default: <name>" synchronously after app init. */
+const osLocaleRef = ref<SupportedLocale | null>(null)
+
+function isSupported(value: string): value is SupportedLocale {
+  return (SUPPORTED_LOCALES as readonly string[]).includes(value)
+}
+
+function normalizeLocale(raw: string | null | undefined): SupportedLocale {
+  if (!raw) return DEFAULT_LOCALE
+  const base = raw.toLowerCase().split('-')[0]
+  return isSupported(base) ? base : DEFAULT_LOCALE
+}
+
+export async function detectOsLocale(): Promise<SupportedLocale> {
+  if (osLocaleRef.value !== null) return osLocaleRef.value
+  try {
+    osLocaleRef.value = normalizeLocale(await osLocaleApi())
+  } catch {
+    osLocaleRef.value = DEFAULT_LOCALE
+  }
+  return osLocaleRef.value
+}
+
+export function useLocale() {
+  const { locale, t } = useI18n()
+  const settings = useSettingsStore()
+
+  /**
+   * Resolve and apply the locale to use at app start. Order:
+   *   1. Persisted user choice (`settings.i18nLocale`) if supported.
+   *   2. OS locale via tauri-plugin-os, region-stripped.
+   *   3. Fallback `en`.
+   *
+   * Always warms the OS-locale cache so the Settings picker can render its
+   * "System default: <name>" label without an extra round-trip.
+   */
+  async function init() {
+    const persisted = settings.i18nLocale
+    if (persisted && isSupported(persisted)) {
+      locale.value = persisted
+      // Warm the OS cache for the Settings picker label even when the
+      // persisted choice overrides it.
+      detectOsLocale().catch(() => {})
+      return
+    }
+    locale.value = await detectOsLocale()
+  }
+
+  /** Switch the active locale. `null` means "follow system" — the persisted
+   *  choice is cleared and the live locale falls back to the OS reading. */
+  async function setLocale(next: SupportedLocale | null) {
+    if (next === null) {
+      await settings.setI18nLocale(null)
+      locale.value = await detectOsLocale()
+      return
+    }
+    await settings.setI18nLocale(next)
+    locale.value = next
+  }
+
+  return { locale, setLocale, init, t, osLocale: osLocaleRef }
+}
diff --git a/locales/en.json b/locales/en.json
new file mode 100644
index 0000000..c6d4417
--- /dev/null
+++ b/locales/en.json
@@ -0,0 +1,34 @@
+{
+  "settings": {
+    "language": {
+      "label": "Language",
+      "description": "UI display language",
+      "system_default": "System default: {name}",
+      "system_default_pending": "System default"
+    }
+  },
+  "nav": {
+    "nodes": "Nodes",
+    "files": "Files",
+    "wallet": "Wallet",
+    "settings": "Settings"
+  },
+  "header": {
+    "title": "Autonomi",
+    "active_transfers": "{count} active",
+    "connecting": "Connecting",
+    "connecting_tooltip": "Connecting to the Autonomi network",
+    "connected": "Network",
+    "connected_tooltip": "Connected to the Autonomi network",
+    "offline": "Offline · Retry",
+    "offline_tooltip": "Connection failed — click to retry",
+    "connect_wallet": "Connect Wallet"
+  },
+  "sidebar": {
+    "pre_release": "PRE-RELEASE",
+    "update_available": "Update Available",
+    "update_pre_release_tag": "Pre-Release",
+    "network_devnet": "DEVNET",
+    "network_sepolia": "SEPOLIA TESTNET"
+  }
+}
diff --git a/locales/ja.json b/locales/ja.json
new file mode 100644
index 0000000..0341e44
--- /dev/null
+++ b/locales/ja.json
@@ -0,0 +1,35 @@
+{
+  "_translator_notes": "Machine-translated baseline. Community polish via PR welcome.",
+  "settings": {
+    "language": {
+      "label": "言語",
+      "description": "UI 表示言語",
+      "system_default": "システムのデフォルト: {name}",
+      "system_default_pending": "システムのデフォルト"
+    }
+  },
+  "nav": {
+    "nodes": "ノード",
+    "files": "ファイル",
+    "wallet": "ウォレット",
+    "settings": "設定"
+  },
+  "header": {
+    "title": "Autonomi",
+    "active_transfers": "{count} 件処理中",
+    "connecting": "接続中",
+    "connecting_tooltip": "Autonomi ネットワークに接続中",
+    "connected": "ネットワーク",
+    "connected_tooltip": "Autonomi ネットワークに接続済み",
+    "offline": "オフライン · 再試行",
+    "offline_tooltip": "接続に失敗しました — クリックして再試行",
+    "connect_wallet": "ウォレットを接続"
+  },
+  "sidebar": {
+    "pre_release": "プレリリース",
+    "update_available": "アップデート利用可能",
+    "update_pre_release_tag": "プレリリース",
+    "network_devnet": "DEVNET",
+    "network_sepolia": "SEPOLIA テストネット"
+  }
+}
diff --git a/package-lock.json b/package-lock.json
index ae4d91b..7816bdf 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "ant-gui",
-  "version": "0.6.7",
+  "version": "0.7.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ant-gui",
-      "version": "0.6.7",
+      "version": "0.7.0",
       "dependencies": {
         "@pinia/nuxt": "^0.5.0",
         "@reown/appkit": "^1.8.19",
@@ -14,6 +14,7 @@
         "@tauri-apps/api": "^2.0.0",
         "@tauri-apps/plugin-dialog": "^2.0.0",
         "@tauri-apps/plugin-opener": "^2.0.0",
+        "@tauri-apps/plugin-os": "^2.3.2",
         "@tauri-apps/plugin-process": "^2.0.0",
         "@tauri-apps/plugin-updater": "^2.0.0",
         "@wagmi/core": "^3.4.0",
@@ -21,6 +22,7 @@
         "pinia": "^2.2.0",
         "viem": "^2.47.1",
         "vue": "^3.5.0",
+        "vue-i18n": "^11.4.2",
         "vue-router": "^4.4.0"
       },
       "devDependencies": {
@@ -1063,6 +1065,67 @@
         "node": ">=18"
       }
     },
+    "node_modules/@intlify/core-base": {
+      "version": "11.4.2",
+      "resolved": "https://registry.npmjs.org/@intlify/core-base/-/core-base-11.4.2.tgz",
+      "integrity": "sha512-7fpuCcVmeLv2T9qHsARqGvh8xt+sV2fH+Q+gMHFwB/rPXzo85DpbJFKn7dBH1L5p0c2cSh2DW+2h/64EKrISmA==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/devtools-types": "11.4.2",
+        "@intlify/message-compiler": "11.4.2",
+        "@intlify/shared": "11.4.2"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/devtools-types": {
+      "version": "11.4.2",
+      "resolved": "https://registry.npmjs.org/@intlify/devtools-types/-/devtools-types-11.4.2.tgz",
+      "integrity": "sha512-3u8EN1kB6EMSi96KXs5k7a8y2X2g4+h3X6iwVZU47cP4n+mTuq//WMjG588BzSp/2XQ/dTXo2BLUXX+XS+PNfA==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/core-base": "11.4.2",
+        "@intlify/shared": "11.4.2"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/message-compiler": {
+      "version": "11.4.2",
+      "resolved": "https://registry.npmjs.org/@intlify/message-compiler/-/message-compiler-11.4.2.tgz",
+      "integrity": "sha512-a6CDSGSMTGrg0BjD97x8TBYPf7qQMDlZipJ6UDfv/pd4OIym8TMlHu3MsH0bTNnRdAG2D6EFEykIgiQPqvtTkA==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/shared": "11.4.2",
+        "source-map-js": "^1.0.2"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/shared": {
+      "version": "11.4.2",
+      "resolved": "https://registry.npmjs.org/@intlify/shared/-/shared-11.4.2.tgz",
+      "integrity": "sha512-NzpHbguRCsOHDwxmlBa9qu/imc+/QWgsYUaK6FZeNC0wK8QfAbhqrktEp/haVzxU1aikH8IX4ytD+mfFEMi/9A==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
     "node_modules/@ioredis/commands": {
       "version": "1.5.1",
       "resolved": "https://registry.npmjs.org/@ioredis/commands/-/commands-1.5.1.tgz",
@@ -5448,6 +5511,15 @@
         "@tauri-apps/api": "^2.8.0"
       }
     },
+    "node_modules/@tauri-apps/plugin-os": {
+      "version": "2.3.2",
+      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-os/-/plugin-os-2.3.2.tgz",
+      "integrity": "sha512-n+nXWeuSeF9wcEsSPmRnBEGrRgOy6jjkSU+UVCOV8YUGKb2erhDOxis7IqRXiRVHhY8XMKks00BJ0OAdkpf6+A==",
+      "license": "MIT OR Apache-2.0",
+      "dependencies": {
+        "@tauri-apps/api": "^2.8.0"
+      }
+    },
     "node_modules/@tauri-apps/plugin-process": {
       "version": "2.3.1",
       "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-process/-/plugin-process-2.3.1.tgz",
@@ -14532,6 +14604,27 @@
       "integrity": "sha512-RutnB7X8c5hjq39NceArgXg28WZtZpGc3+J16ljMiYnFhKvd8hITxSWQSQ5bvldxMDU6gG5mkxl1MTQLXckVSQ==",
       "license": "MIT"
     },
+    "node_modules/vue-i18n": {
+      "version": "11.4.2",
+      "resolved": "https://registry.npmjs.org/vue-i18n/-/vue-i18n-11.4.2.tgz",
+      "integrity": "sha512-sADDeKXqAGsPX6tK3t3y2ZiMpbVWN12tG+MhTiJ06rVoh58eGtM4wFyw3uWGbVkXByVp9Ne/AP+nSSzI+J9OAQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/core-base": "11.4.2",
+        "@intlify/devtools-types": "11.4.2",
+        "@intlify/shared": "11.4.2",
+        "@vue/devtools-api": "^6.5.0"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      },
+      "peerDependencies": {
+        "vue": "^3.0.0"
+      }
+    },
     "node_modules/vue-router": {
       "version": "4.6.4",
       "resolved": "https://registry.npmjs.org/vue-router/-/vue-router-4.6.4.tgz",
diff --git a/package.json b/package.json
index 27d5e17..edfcefe 100644
--- a/package.json
+++ b/package.json
@@ -20,6 +20,7 @@
     "@tauri-apps/api": "^2.0.0",
     "@tauri-apps/plugin-dialog": "^2.0.0",
     "@tauri-apps/plugin-opener": "^2.0.0",
+    "@tauri-apps/plugin-os": "^2.3.2",
     "@tauri-apps/plugin-process": "^2.0.0",
     "@tauri-apps/plugin-updater": "^2.0.0",
     "@wagmi/core": "^3.4.0",
@@ -27,6 +28,7 @@
     "pinia": "^2.2.0",
     "viem": "^2.47.1",
     "vue": "^3.5.0",
+    "vue-i18n": "^11.4.2",
     "vue-router": "^4.4.0"
   },
   "devDependencies": {
diff --git a/pages/settings.vue b/pages/settings.vue
index 706fffd..4038985 100644
--- a/pages/settings.vue
+++ b/pages/settings.vue
@@ -107,6 +107,23 @@
       </button>
     </div>
 
+    <!-- Language -->
+    <div class="flex items-center justify-between rounded-lg border border-autonomi-border p-4">
+      <div class="min-w-0 flex-1">
+        <h3 class="text-sm font-medium">{{ $t('settings.language.label') }}</h3>
+        <p class="text-xs text-autonomi-muted">{{ $t('settings.language.description') }}</p>
+      </div>
+      <select
+        v-model="localeChoice"
+        :aria-label="$t('settings.language.label')"
+        class="ml-3 shrink-0 rounded-md border border-autonomi-border bg-autonomi-dark px-3 py-1.5 text-xs text-autonomi-text focus:border-autonomi-blue focus:outline-none"
+      >
+        <option value="system">{{ systemDefaultLabel }}</option>
+        <option value="en">English</option>
+        <option value="ja">日本語</option>
+      </select>
+    </div>
+
     <!-- Advanced -->
     <div>
       <button
@@ -506,6 +523,7 @@ import { openUrl as tauriOpenUrl } from '@tauri-apps/plugin-opener'
 import { arbitrum, arbitrumSepolia } from 'viem/chains'
 import { setDevnetWalletKey, UPLOAD_CONCURRENCY_MIN, UPLOAD_CONCURRENCY_MAX } from '~/stores/settings'
 import { useSettingsStore } from '~/stores/settings'
+import { useLocale, SUPPORTED_LOCALES, NATIVE_LOCALE_NAMES, type SupportedLocale } from '~/composables/useLocale'
 import { isValidEthAddress } from '~/utils/validators'
 import { useToastStore } from '~/stores/toasts'
 import { useErrorLogStore } from '~/stores/errorlog'
@@ -513,6 +531,31 @@ import { useUpdaterStore } from '~/stores/updater'
 import { useFilesStore } from '~/stores/files'
 
 const settingsStore = useSettingsStore()
+const { setLocale, osLocale, t } = useLocale()
+
+/** Bound to the Language <select>. `'system'` is the sentinel for "follow
+ *  the OS locale" (persisted as null in config.toml). */
+const localeChoice = computed<'system' | SupportedLocale>({
+  get: () => {
+    const persisted = settingsStore.i18nLocale
+    return persisted && (SUPPORTED_LOCALES as readonly string[]).includes(persisted)
+      ? (persisted as SupportedLocale)
+      : 'system'
+  },
+  set: (value) => {
+    setLocale(value === 'system' ? null : value)
+  },
+})
+
+/** Label for the "Follow system" option. Shows the detected OS-locale's
+ *  native name once detection resolves (e.g. "System default: English"),
+ *  falling back to the bare label during the brief pre-detection window. */
+const systemDefaultLabel = computed(() =>
+  osLocale.value
+    ? t('settings.language.system_default', { name: NATIVE_LOCALE_NAMES[osLocale.value] })
+    : t('settings.language.system_default_pending'),
+)
+
 const walletStore = useWalletStore()
 const nodesStore = useNodesStore()
 const toasts = useToastStore()
diff --git a/plugins/i18n.client.ts b/plugins/i18n.client.ts
new file mode 100644
index 0000000..c9d7e50
--- /dev/null
+++ b/plugins/i18n.client.ts
@@ -0,0 +1,21 @@
+import { createI18n } from 'vue-i18n'
+import en from '~/locales/en.json'
+import ja from '~/locales/ja.json'
+
+export default defineNuxtPlugin((nuxtApp) => {
+  const i18n = createI18n({
+    legacy: false,
+    locale: 'en',
+    fallbackLocale: 'en',
+    messages: { en, ja },
+    missingWarn: true,
+    fallbackWarn: false,
+  })
+  nuxtApp.vueApp.use(i18n)
+
+  // Dev-only handle for manual locale-swap testing from DevTools console.
+  // Remove when the Settings picker lands.
+  if (import.meta.dev && typeof window !== 'undefined') {
+    ;(window as unknown as { __i18n: typeof i18n }).__i18n = i18n
+  }
+})
diff --git a/src-tauri/Cargo.lock b/src-tauri/Cargo.lock
index ae5adc7..718ec17 100644
--- a/src-tauri/Cargo.lock
+++ b/src-tauri/Cargo.lock
@@ -863,6 +863,7 @@ dependencies = [
  "tauri-build",
  "tauri-plugin-dialog",
  "tauri-plugin-opener",
+ "tauri-plugin-os",
  "tauri-plugin-process",
  "tauri-plugin-updater",
  "tokio",
@@ -3351,6 +3352,16 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "gethostname"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bd49230192a3797a9a4d6abe9b3eed6f7fa4c8a8a4947977c6f80025f92cbd8"
+dependencies = [
+ "rustix",
+ "windows-link 0.2.1",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.1.16"
@@ -4745,6 +4756,18 @@ dependencies = [
  "memoffset",
 ]
 
+[[package]]
+name = "nix"
+version = "0.30.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "74523f3a35e05aba87a1d978330aef40f67b0304ac79c1c00b294c9830543db6"
+dependencies = [
+ "bitflags 2.11.1",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "nodrop"
 version = "0.1.14"
@@ -4892,6 +4915,27 @@ dependencies = [
  "objc2-foundation",
 ]
 
+[[package]]
+name = "objc2-cloud-kit"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73ad74d880bb43877038da939b7427bba67e9dd42004a18b809ba7d87cee241c"
+dependencies = [
+ "bitflags 2.11.1",
+ "objc2",
+ "objc2-foundation",
+]
+
+[[package]]
+name = "objc2-core-data"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b402a653efbb5e82ce4df10683b6b28027616a2715e90009947d50b8dd298fa"
+dependencies = [
+ "objc2",
+ "objc2-foundation",
+]
+
 [[package]]
 name = "objc2-core-foundation"
 version = "0.3.2"
@@ -4916,6 +4960,38 @@ dependencies = [
  "objc2-io-surface",
 ]
 
+[[package]]
+name = "objc2-core-image"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5d563b38d2b97209f8e861173de434bd0214cf020e3423a52624cd1d989f006"
+dependencies = [
+ "objc2",
+ "objc2-foundation",
+]
+
+[[package]]
+name = "objc2-core-location"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca347214e24bc973fc025fd0d36ebb179ff30536ed1f80252706db19ee452009"
+dependencies = [
+ "objc2",
+ "objc2-foundation",
+]
+
+[[package]]
+name = "objc2-core-text"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0cde0dfb48d25d2b4862161a4d5fcc0e3c24367869ad306b0c9ec0073bfed92d"
+dependencies = [
+ "bitflags 2.11.1",
+ "objc2",
+ "objc2-core-foundation",
+ "objc2-core-graphics",
+]
+
 [[package]]
 name = "objc2-encode"
 version = "4.1.0"
@@ -4986,8 +5062,27 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d87d638e33c06f577498cbcc50491496a3ed4246998a7fbba7ccb98b1e7eab22"
 dependencies = [
  "bitflags 2.11.1",
+ "block2",
  "objc2",
+ "objc2-cloud-kit",
+ "objc2-core-data",
  "objc2-core-foundation",
+ "objc2-core-graphics",
+ "objc2-core-image",
+ "objc2-core-location",
+ "objc2-core-text",
+ "objc2-foundation",
+ "objc2-quartz-core",
+ "objc2-user-notifications",
+]
+
+[[package]]
+name = "objc2-user-notifications"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9df9128cbbfef73cda168416ccf7f837b62737d748333bfe9ab71c245d76613e"
+dependencies = [
+ "objc2",
  "objc2-foundation",
 ]
 
@@ -5114,6 +5209,22 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "os_info"
+version = "3.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e4022a17595a00d6a369236fdae483f0de7f0a339960a53118b818238e132224"
+dependencies = [
+ "android_system_properties",
+ "log",
+ "nix 0.30.1",
+ "objc2",
+ "objc2-foundation",
+ "objc2-ui-kit",
+ "serde",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "osakit"
 version = "0.3.1"
@@ -6711,7 +6822,7 @@ dependencies = [
  "keyring",
  "libc",
  "lru-slab",
- "nix",
+ "nix 0.29.0",
  "once_cell",
  "parking_lot",
  "pin-project-lite",
@@ -7564,6 +7675,15 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "sys-locale"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8eab9a99a024a169fe8a903cf9d4a3b3601109bcc13bd9e3c6fff259138626c4"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "sysinfo"
 version = "0.32.1"
@@ -7889,6 +8009,24 @@ dependencies = [
  "zbus",
 ]
 
+[[package]]
+name = "tauri-plugin-os"
+version = "2.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8f08346c8deb39e96f86973da0e2d76cbb933d7ac9b750f6dc4daf955a6f997"
+dependencies = [
+ "gethostname",
+ "log",
+ "os_info",
+ "serde",
+ "serde_json",
+ "serialize-to-javascript",
+ "sys-locale",
+ "tauri",
+ "tauri-plugin",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "tauri-plugin-process"
 version = "2.3.1"
diff --git a/src-tauri/Cargo.toml b/src-tauri/Cargo.toml
index 8eb9dc1..35b495c 100644
--- a/src-tauri/Cargo.toml
+++ b/src-tauri/Cargo.toml
@@ -14,6 +14,7 @@ tauri-build = { version = "2", features = [] }
 tauri = { version = "2", features = [] }
 tauri-plugin-dialog = "2"
 tauri-plugin-opener = "2"
+tauri-plugin-os = "2"
 tauri-plugin-process = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
diff --git a/src-tauri/capabilities/default.json b/src-tauri/capabilities/default.json
index d6a7027..8a2cf4f 100644
--- a/src-tauri/capabilities/default.json
+++ b/src-tauri/capabilities/default.json
@@ -11,6 +11,8 @@
     "dialog:allow-ask",
     "opener:default",
     "opener:allow-reveal-item-in-dir",
+    "os:default",
+    "os:allow-locale",
     "process:default",
     "updater:default",
     "updater:allow-check",
diff --git a/src-tauri/src/config.rs b/src-tauri/src/config.rs
index 4755cc8..8c99a2f 100644
--- a/src-tauri/src/config.rs
+++ b/src-tauri/src/config.rs
@@ -35,6 +35,11 @@ pub struct AppConfig {
     /// init from this flag, so toggling requires an app restart to take effect.
     #[serde(default)]
     pub prerelease_channel: bool,
+    /// User-chosen UI locale (e.g. "en", "ja"). `None` means "follow system":
+    /// the frontend reads the OS locale via tauri-plugin-os and falls back to
+    /// English if it doesn't match a shipped locale.
+    #[serde(default)]
+    pub i18n_locale: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -132,6 +137,7 @@ impl Default for AppConfig {
             theme_mode: default_theme_mode(),
             upload_concurrency: default_upload_concurrency(),
             prerelease_channel: false,
+            i18n_locale: None,
         }
     }
 }
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 43e35f3..355281b 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -743,6 +743,7 @@ pub fn run() {
     tauri::Builder::default()
         .plugin(tauri_plugin_dialog::init())
         .plugin(tauri_plugin_opener::init())
+        .plugin(tauri_plugin_os::init())
         .plugin(tauri_plugin_process::init())
         .plugin(tauri_plugin_updater::Builder::new().build())
         .manage(AutonomiState::new())
diff --git a/stores/settings.ts b/stores/settings.ts
index 9076b6c..8ae5d4a 100644
--- a/stores/settings.ts
+++ b/stores/settings.ts
@@ -33,6 +33,7 @@ interface AppConfig {
   theme_mode: string
   upload_concurrency: number
   prerelease_channel: boolean
+  i18n_locale: string | null
 }
 
 /** Allowed range for upload_concurrency (see AppConfig in Rust). */
@@ -67,6 +68,8 @@ export const useSettingsStore = defineStore('settings', {
     /** Snapshot of `prereleaseChannel` at app boot — drives the "restart to
      *  apply" hint banner. Set once during loadConfig. */
     prereleaseChannelBootValue: false,
+    /** Persisted UI locale choice. `null` = follow the OS. */
+    i18nLocale: null as string | null,
     loaded: false,
     // Devnet/testnet/direct-key mode (set by manifest or settings form).
     // devnetChainId picks the chain:
@@ -99,6 +102,7 @@ export const useSettingsStore = defineStore('settings', {
         this.themeMode = config.theme_mode === 'light' ? 'light' : 'dark'
         this.uploadConcurrency = clampConcurrency(config.upload_concurrency)
         this.prereleaseChannel = config.prerelease_channel ?? false
+        this.i18nLocale = config.i18n_locale ?? null
         // Capture once on first load — represents the value the Rust side
         // resolved its updater endpoint URL from. Subsequent toggles diverge
         // from this until the next app restart.
@@ -122,6 +126,7 @@ export const useSettingsStore = defineStore('settings', {
           theme_mode: this.themeMode,
           upload_concurrency: this.uploadConcurrency,
           prerelease_channel: this.prereleaseChannel,
+          i18n_locale: this.i18nLocale,
         }
         await invoke('save_config', { config })
       } catch (e) {
@@ -169,6 +174,12 @@ export const useSettingsStore = defineStore('settings', {
       await this.saveConfig()
     },
 
+    /** Persist UI-locale choice. `null` means "follow the OS locale". */
+    async setI18nLocale(locale: string | null) {
+      this.i18nLocale = locale
+      await this.saveConfig()
+    },
+
     async testIndelibleConnection(url: string, apiKey: string): Promise<{ ok: boolean; error?: string }> {
       try {
         const baseUrl = url.replace(/\/+$/, '').replace(/\/api\/v2.*$/, '')