diff --git a/packages/client-ui/src/components/common/BottomToast.test.ts b/packages/client-ui/src/components/common/BottomToast.test.ts
index cf868ba..2dec186 100644
--- a/packages/client-ui/src/components/common/BottomToast.test.ts
+++ b/packages/client-ui/src/components/common/BottomToast.test.ts
@@ -1,5 +1,9 @@
 import { mount } from '@vue/test-utils'
 import { describe, expect, it } from 'vitest'
+import { nextTick } from 'vue'
+import { createBottomToast } from '../../composables/useBottomToast'
+import { setLocale, t } from '../../i18n'
+import { bottomToastKey } from '../../runtimeKey'
 import BottomToast from './BottomToast.vue'
 
 describe('BottomToast', () => {
@@ -10,4 +14,35 @@ describe('BottomToast', () => {
     expect(wrapper.get('[data-bottom-toast]').attributes('role')).toBe('status')
     expect(wrapper.get('[data-bottom-toast]').attributes('data-tone')).toBe('success')
   })
+
+  it('reactively translates visible bottom toast when locale toggles between zh and en', async () => {
+    setLocale('zh')
+    const controller = createBottomToast({
+      now: () => 0,
+      setTimeout: () => 1,
+      clearTimeout: () => {},
+      setInterval: () => 1,
+      clearInterval: () => {},
+    })
+    controller.show({ text: () => t('agent.chat.forbiddenToast'), tone: 'error' })
+
+    const wrapper = mount(BottomToast, {
+      global: {
+        provide: {
+          [bottomToastKey as symbol]: controller,
+        },
+      },
+    })
+
+    expect(wrapper.get('[data-bottom-toast]').text()).toBe('当前客户端没有访问该会话的权限，请重新登录授权。')
+    setLocale('en')
+    await nextTick()
+    try {
+      expect(wrapper.get('[data-bottom-toast]').text()).toBe('This client does not have permission to access this session. Please sign in and authorize again.')
+    } finally {
+      setLocale('zh')
+      await nextTick()
+    }
+    expect(wrapper.get('[data-bottom-toast]').text()).toBe('当前客户端没有访问该会话的权限，请重新登录授权。')
+  })
 })
diff --git a/packages/client-ui/src/components/common/BottomToast.vue b/packages/client-ui/src/components/common/BottomToast.vue
index c4f3b3e..295672f 100644
--- a/packages/client-ui/src/components/common/BottomToast.vue
+++ b/packages/client-ui/src/components/common/BottomToast.vue
@@ -11,6 +11,7 @@
 <script setup lang="ts">
 import { computed, inject } from 'vue'
 import type { BottomToastMessage, BottomToastTone } from '../../composables/useBottomToast'
+import { useI18n } from '../../i18n'
 import { bottomToastKey } from '../../runtimeKey'
 
 const props = defineProps<{
@@ -18,9 +19,11 @@ const props = defineProps<{
   tone?: BottomToastTone
 }>()
 
+const { locale, translateDynamicText } = useI18n()
 const controller = inject(bottomToastKey, undefined)
 const active = computed<BottomToastMessage | null>(() => {
-  if (props.message !== undefined) return { text: props.message, tone: props.tone ?? 'success' }
+  void locale.value
+  if (props.message !== undefined) return { text: translateDynamicText(props.message), tone: props.tone ?? 'success' }
   return controller?.current.value ?? null
 })
 </script>
diff --git a/packages/client-ui/src/composables/useAgentConversation.ts b/packages/client-ui/src/composables/useAgentConversation.ts
index 116f571..0a41939 100644
--- a/packages/client-ui/src/composables/useAgentConversation.ts
+++ b/packages/client-ui/src/composables/useAgentConversation.ts
@@ -118,16 +118,16 @@ export function useAgentConversation(options: UseAgentConversationOptions) {
         }
         if (info.code === AGENT_STREAM_CLOSE_NOT_FOUND) {
           runtime.agentCursorStore.clear(options.conversationId)
-          toast.show({ text: t('agent.chat.notFoundToast'), tone: 'error' })
+          toast.show({ text: () => t('agent.chat.notFoundToast'), tone: 'error' })
           return
         }
         if (info.code === AGENT_STREAM_CLOSE_FORBIDDEN) {
-          toast.show({ text: t('agent.chat.forbiddenToast'), tone: 'error' })
+          toast.show({ text: () => t('agent.chat.forbiddenToast'), tone: 'error' })
         }
       },
       onError: (error) => {
         if (error.code === 'stream_too_slow') {
-          toast.show({ text: t('agent.chat.recoveringToast'), tone: 'error' })
+          toast.show({ text: () => t('agent.chat.recoveringToast'), tone: 'error' })
         }
       },
       onAuthenticationRequired: handleAuthenticationRequired,
diff --git a/packages/client-ui/src/composables/useAgentConversations.ts b/packages/client-ui/src/composables/useAgentConversations.ts
index 6a8c0dd..df2b273 100644
--- a/packages/client-ui/src/composables/useAgentConversations.ts
+++ b/packages/client-ui/src/composables/useAgentConversations.ts
@@ -7,7 +7,7 @@
 import type { AgentConversationResponse } from '@termflow/client-contracts'
 import { ApiError, createApprovalsApi } from '@termflow/client-core'
 import { onBeforeUnmount, onMounted, ref, toValue, watch, type MaybeRefOrGetter } from 'vue'
-import { t } from '../i18n'
+import { locale, t, translateDynamicText } from '../i18n'
 import { useClientRuntime } from '../runtime'
 import { useBottomToast } from './useBottomToast'
 
@@ -26,6 +26,11 @@ export function useAgentConversations(bindingId?: MaybeRefOrGetter<BindingScope>
   const pendingCounts = ref<ReadonlyMap<string, number>>(new Map())
   const loading = ref(true)
   const errorMessage = ref<string | null>(null)
+  watch(locale, () => {
+    if (errorMessage.value !== null) {
+      errorMessage.value = translateDynamicText(errorMessage.value)
+    }
+  })
   const approvalsApi = createApprovalsApi(runtime.api.request)
   // List loads and mutations keep separate controllers: load() aborts its
   // own in-flight list request on a binding switch, which must not cancel
diff --git a/packages/client-ui/src/composables/useBottomToast.ts b/packages/client-ui/src/composables/useBottomToast.ts
index c44f425..3cd3df7 100644
--- a/packages/client-ui/src/composables/useBottomToast.ts
+++ b/packages/client-ui/src/composables/useBottomToast.ts
@@ -1,4 +1,5 @@
-import { inject, ref, type Ref } from 'vue'
+import { computed, inject, ref, type Ref } from 'vue'
+import { locale, translateDynamicText } from '../i18n'
 import type { ClockPort } from '../runtime'
 import { bottomToastKey } from '../runtimeKey'
 
@@ -9,25 +10,39 @@ export interface BottomToastMessage {
   readonly tone: BottomToastTone
 }
 
+export interface BottomToastInput {
+  readonly text: string | (() => string)
+  readonly tone: BottomToastTone
+}
+
 export interface BottomToastController {
   readonly current: Readonly<Ref<BottomToastMessage | null>>
-  show(message: BottomToastMessage): void
+  show(message: BottomToastInput): void
   clear(): void
 }
 
 export function createBottomToast(clock: ClockPort): BottomToastController {
-  const current = ref<BottomToastMessage | null>(null)
+  const rawCurrent = ref<BottomToastInput | null>(null)
+  const current = computed<BottomToastMessage | null>(() => {
+    void locale.value
+    if (rawCurrent.value === null) return null
+    const rawText = typeof rawCurrent.value.text === 'function' ? rawCurrent.value.text() : rawCurrent.value.text
+    return {
+      text: translateDynamicText(rawText),
+      tone: rawCurrent.value.tone,
+    }
+  })
   let timer: unknown | null = null
   function clear() {
     if (timer !== null) clock.clearTimeout(timer)
     timer = null
-    current.value = null
+    rawCurrent.value = null
   }
-  function show(message: BottomToastMessage) {
+  function show(message: BottomToastInput) {
     clear()
-    current.value = message
+    rawCurrent.value = message
     timer = clock.setTimeout(() => {
-      current.value = null
+      rawCurrent.value = null
       timer = null
     }, 3_000)
   }
diff --git a/packages/client-ui/src/i18n/index.ts b/packages/client-ui/src/i18n/index.ts
index 007d35b..a4ec61d 100644
--- a/packages/client-ui/src/i18n/index.ts
+++ b/packages/client-ui/src/i18n/index.ts
@@ -297,6 +297,7 @@ const messages: Record<Locale, Record<string, string>> = {
     'login.totpHint': '（请输入验证器应用当前显示的 6 位验证码。）',
     'login.submit': '登录',
     'login.verifyAndLogin': '验证并登录',
+    'login.invalidToken': '管理员令牌无效，请核对后重试。',
     'login.failed': '登录失败，请重试。',
     'deviceAuth.eyebrow': '跨设备授权',
     'deviceAuth.title': '授权新设备',
@@ -825,6 +826,7 @@ const messages: Record<Locale, Record<string, string>> = {
     'login.totpHint': ' (Enter the 6-digit code from your authenticator app.)',
     'login.submit': 'Sign In',
     'login.verifyAndLogin': 'Verify & Sign In',
+    'login.invalidToken': 'Invalid admin token. Please check and try again.',
     'login.failed': 'Sign-in failed. Please try again.',
     'deviceAuth.eyebrow': 'Cross-device authorization',
     'deviceAuth.title': 'Authorize New Device',
@@ -1122,6 +1124,25 @@ export function t(key: string, params?: Record<string, string | number>): string
   })
 }
 
+const reverseKeyMap = new Map<string, string>()
+for (const [key, val] of Object.entries(messages.zh)) {
+  if (!val.includes('{')) reverseKeyMap.set(val, key)
+}
+for (const [key, val] of Object.entries(messages.en)) {
+  if (!val.includes('{')) reverseKeyMap.set(val, key)
+}
+
+export function translateDynamicText(text: string): string {
+  if (!text) return text
+  const dict = messages[currentLocale.value] ?? messages.zh
+  if (dict[text] !== undefined) return dict[text]
+  const matchedKey = reverseKeyMap.get(text)
+  if (matchedKey !== undefined && dict[matchedKey] !== undefined) {
+    return dict[matchedKey]
+  }
+  return text
+}
+
 export function useI18n() {
   const stored = readStoredLocale()
   if (stored !== null && currentLocale.value !== stored) {
@@ -1133,5 +1154,6 @@ export function useI18n() {
     setLocale,
     toggleLocale,
     t,
+    translateDynamicText,
   }
 }
diff --git a/packages/client-ui/src/views/AgentPreviewView.vue b/packages/client-ui/src/views/AgentPreviewView.vue
index 6a52822..8dbf95e 100644
--- a/packages/client-ui/src/views/AgentPreviewView.vue
+++ b/packages/client-ui/src/views/AgentPreviewView.vue
@@ -10,6 +10,17 @@
       </div>
       <div class="agent-chat-header__actions">
         <span class="agent-backend-status agent-backend-status--busy">{{ t('agent.backend.busy') }}</span>
+        <button
+          data-action="toggle-locale"
+          class="text-button locale-toggle-button"
+          type="button"
+          :aria-label="t('app.switchLangAria')"
+          :title="t('app.switchLangAria')"
+          @click="toggleLocale"
+        >
+          <Globe :size="15" aria-hidden="true" />
+          <span class="locale-badge">{{ t('app.switchLangBadge') }}</span>
+        </button>
       </div>
     </header>
     <div class="agent-chat-body">
@@ -50,7 +61,7 @@ import AgentApprovalCard from '../components/agent/AgentApprovalCard.vue'
 import AgentPartsList, { type AgentConversationPart } from '../components/agent/AgentPartsList.vue'
 import MobileKeyBar from '../components/terminal/MobileKeyBar.vue'
 import ThemePicker from '../components/settings/ThemePicker.vue'
-import { Send } from '@lucide/vue'
+import { Globe, Send } from '@lucide/vue'
 import { useSensitiveAuthorization } from '../composables/useSensitiveAuthorization'
 import { useI18n } from '../i18n'
 import {
@@ -62,7 +73,7 @@ import {
   type AguiEvent,
 } from '@termflow/client-core'
 
-const { t } = useI18n()
+const { t, locale, toggleLocale } = useI18n()
 const authorization = useSensitiveAuthorization()
 const modifierController = new MobileModifierController()
 const lastKeyInput = ref('')
@@ -70,56 +81,61 @@ function handleKeyInput(bytes: Uint8Array) {
   lastKeyInput.value = new TextDecoder().decode(bytes)
 }
 const now = Date.now()
-let state = createAgentHistoryState()
-state = seedUserMessages(
-  state,
-  [
+const history = computed<AgentHistoryState>(() => {
+  void locale.value
+  let state = createAgentHistoryState()
+  state = seedUserMessages(
+    state,
+    [
+      {
+        message_id: 'u1',
+        conversation_id: 'c1',
+        run_id: null,
+        role: 'user',
+        kind: 'text',
+        assembly_revision: 1,
+        is_final: false,
+        body_digest: 'd',
+        body: t('agent.preview.sampleUserPrompt'),
+        created_at: new Date(now).toISOString(),
+      },
+    ] as never,
+    () => now,
+  )
+
+  const frames: AguiEvent[] = [
+    { type: 'RUN_STARTED', threadId: 'c1', runId: 'r1' },
+    { type: 'STATE_DELTA', delta: [{ op: 'replace', path: '/backend', value: { state: 'busy', epoch: 1 } }] },
+    { type: 'CUSTOM', name: 'termflow.thinking_delta', value: { id: 'th1', delta: t('agent.preview.sampleThinking1') } },
+    { type: 'CUSTOM', name: 'termflow.thinking_completed', value: { id: 'th1' } },
+    { type: 'TEXT_MESSAGE_CHUNK', messageId: 'a1', delta: t('agent.preview.sampleAssistant1') },
+    { type: 'TOOL_CALL_START', toolCallId: 't1', toolCallName: 'termflow_termflow_list_panes' },
     {
-      message_id: 'u1',
-      conversation_id: 'c1',
-      run_id: null,
-      role: 'user',
-      kind: 'text',
-      assembly_revision: 1,
-      is_final: false,
-      body_digest: 'd',
-      body: t('agent.preview.sampleUserPrompt'),
-      created_at: new Date(now).toISOString(),
+      type: 'TOOL_CALL_RESULT',
+      messageId: 't1',
+      toolCallId: 't1',
+      content: '{"status":"success","truncated":false}',
     },
-  ] as never,
-  () => now,
-)
-
-const frames: AguiEvent[] = [
-  { type: 'RUN_STARTED', threadId: 'c1', runId: 'r1' },
-  { type: 'STATE_DELTA', delta: [{ op: 'replace', path: '/backend', value: { state: 'busy', epoch: 1 } }] },
-  { type: 'CUSTOM', name: 'termflow.thinking_delta', value: { id: 'th1', delta: t('agent.preview.sampleThinking1') } },
-  { type: 'CUSTOM', name: 'termflow.thinking_completed', value: { id: 'th1' } },
-  { type: 'TEXT_MESSAGE_CHUNK', messageId: 'a1', delta: t('agent.preview.sampleAssistant1') },
-  { type: 'TOOL_CALL_START', toolCallId: 't1', toolCallName: 'termflow_termflow_list_panes' },
-  {
-    type: 'TOOL_CALL_RESULT',
-    messageId: 't1',
-    toolCallId: 't1',
-    content: '{"status":"success","truncated":false}',
-  },
-  { type: 'TEXT_MESSAGE_END', messageId: 'a1' },
-  { type: 'TEXT_MESSAGE_CHUNK', messageId: 'a2', delta: t('agent.preview.sampleAssistant2') },
-  {
-    type: 'CUSTOM',
-    name: 'termflow.permission_requested',
-    value: { approval_request_id: 'a0000000-0000-4000-8000-000000000001' },
-  },
-] as AguiEvent[]
-
-for (const frame of frames) state = applyAguiEvent(state, frame, () => now)
+    { type: 'TEXT_MESSAGE_END', messageId: 'a1' },
+    { type: 'TEXT_MESSAGE_CHUNK', messageId: 'a2', delta: t('agent.preview.sampleAssistant2') },
+    {
+      type: 'CUSTOM',
+      name: 'termflow.permission_requested',
+      value: { approval_request_id: 'a0000000-0000-4000-8000-000000000001' },
+    },
+  ] as AguiEvent[]
 
-const history: AgentHistoryState = state
-const parts = computed<AgentConversationPart[]>(() => [
-  { type: 'step-start' },
-  { type: 'reasoning', text: t('agent.preview.sampleThinking1') },
-  { type: 'tool', tool: 'termflow_termflow_list_panes', status: 'completed', input: '{}', output: '{\n  "instance_id": "a38adddd-f204-4bd8-9587-0b57aa21524c",\n  "panes": [{"pane_id": "%0", "active": true, "dead": false}]\n}' },
-  { type: 'reasoning', text: t('agent.preview.sampleThinking2') },
+  for (const frame of frames) state = applyAguiEvent(state, frame, () => now)
+  return state
+})
+void history.value
+const parts = computed<AgentConversationPart[]>(() => {
+  void locale.value
+  return [
+    { type: 'step-start' },
+    { type: 'reasoning', text: t('agent.preview.sampleThinking1') },
+    { type: 'tool', tool: 'termflow_termflow_list_panes', status: 'completed', input: '{}', output: '{\n  "instance_id": "a38adddd-f204-4bd8-9587-0b57aa21524c",\n  "panes": [{"pane_id": "%0", "active": true, "dead": false}]\n}' },
+    { type: 'reasoning', text: t('agent.preview.sampleThinking2') },
   {
     type: 'tool',
     tool: 'termflow_termflow_git_diff',
@@ -149,7 +165,8 @@ const parts = computed<AgentConversationPart[]>(() => [
   { type: 'tool', tool: 'termflow_termflow_pane_read', status: 'completed', input: '{"params": {"pane_id": "%0"}}', output: '"$ echo 1\\n1\\n$ "' },
   { type: 'text', text: t('agent.preview.sampleFinalText') },
   { type: 'step-finish' },
-])
+  ]
+})
 const permission = {
   approvalId: 'a0000000-0000-4000-8000-000000000001',
   toolName: 'rm',
diff --git a/packages/client-ui/src/views/AgentView.vue b/packages/client-ui/src/views/AgentView.vue
index c45d222..eb9feeb 100644
--- a/packages/client-ui/src/views/AgentView.vue
+++ b/packages/client-ui/src/views/AgentView.vue
@@ -162,7 +162,7 @@ import { useBottomToast } from '../composables/useBottomToast'
 import { useI18n } from '../i18n'
 import { useClientRuntime } from '../runtime'
 
-const { t } = useI18n()
+const { t, locale, translateDynamicText } = useI18n()
 const runtime = useClientRuntime()
 const toast = useBottomToast()
 const { agentBrokerEnabled } = useAgentBroker()
@@ -171,6 +171,11 @@ const bindings = ref<AgentBindingResponse[]>([])
 const termNames = ref(new Map<string, string>())
 const directoryLoading = ref(true)
 const directoryError = ref<string | null>(null)
+watch(locale, () => {
+  if (directoryError.value !== null) {
+    directoryError.value = translateDynamicText(directoryError.value)
+  }
+})
 const controller = ref<AbortController | null>(null)
 
 const conversations = useAgentConversations(() => bindings.value.map((binding) => binding.binding_id))
diff --git a/packages/client-ui/src/views/LoginView.test.ts b/packages/client-ui/src/views/LoginView.test.ts
index e42dcb8..16c3df0 100644
--- a/packages/client-ui/src/views/LoginView.test.ts
+++ b/packages/client-ui/src/views/LoginView.test.ts
@@ -118,4 +118,25 @@ describe('LoginView', () => {
     }
     expect(wrapper.get('[role="alert"]').text()).toBe('会话已过期，请重新登录。')
   })
+
+  it('displays invalid admin token error on HTTP 401 unauthorized login failure across zh and en', async () => {
+    const login = vi.fn().mockRejectedValue(new ApiError('authentication', { status: 401, code: 'unauthorized' }))
+    const runtime = createFakeRuntime({ api: { sessions: { login } } as unknown as ClientRuntime['api'] })
+    const { wrapper } = await mountLogin(runtime)
+
+    await wrapper.get('input[type="password"]').setValue('wrong-token')
+    await wrapper.get('form').trigger('submit')
+    await flushPromises()
+    expect(wrapper.get('[role="alert"]').text()).toBe('管理员令牌无效，请核对后重试。')
+
+    const toggleBtn = wrapper.get('[data-action="toggle-locale"]')
+    await toggleBtn.trigger('click')
+    await flushPromises()
+    try {
+      expect(wrapper.get('[role="alert"]').text()).toBe('Invalid admin token. Please check and try again.')
+    } finally {
+      await toggleBtn.trigger('click')
+      await flushPromises()
+    }
+  })
 })
diff --git a/packages/client-ui/src/views/LoginView.vue b/packages/client-ui/src/views/LoginView.vue
index 9b8a2bc..2fead5c 100644
--- a/packages/client-ui/src/views/LoginView.vue
+++ b/packages/client-ui/src/views/LoginView.vue
@@ -76,7 +76,15 @@ async function submit() {
     const requested = typeof route.query.redirect === 'string' ? route.query.redirect : '/'
     await router.replace(requested.startsWith('/') && !requested.startsWith('//') ? requested : '/')
   } catch (error) {
-    errorState.value = error instanceof ApiError ? { type: 'api', kind: error.kind } : { type: 'key', key: 'login.failed' }
+    if (error instanceof ApiError) {
+      if (challengeId.value === null && error.kind === 'authentication' && (error.status === 401 || error.code === 'unauthorized')) {
+        errorState.value = { type: 'key', key: 'login.invalidToken' }
+      } else {
+        errorState.value = { type: 'api', kind: error.kind }
+      }
+    } else {
+      errorState.value = { type: 'key', key: 'login.failed' }
+    }
   } finally {
     adminToken.value = ''
     totpCode.value = ''