feat(im): follow user reply language with session fallback

frontend/src/api/agent/index.ts

@@ -356,6 +356,7 @@ export interface IMChannel {
   mode: 'webhook' | 'websocket' | 'longpoll';
   output_mode: 'stream' | 'full';
   locale?: '' | 'zh-CN' | 'zh-TW' | 'en-US' | 'ko-KR' | 'ja-JP' | 'ru-RU';
+  language_mode?: 'fixed' | 'follow_user';
   session_mode?: 'user' | 'thread';
   knowledge_base_id?: string;
   credentials: Record<string, any>;
@@ -380,6 +381,7 @@ export interface IMChannelOverview {
   mode: IMChannel['mode'];
   output_mode: IMChannel['output_mode'];
   locale?: IMChannel['locale'];
+  language_mode?: IMChannel['language_mode'];
   session_mode?: IMChannel['session_mode'];
   bot_identity: string;
   created_at: string;

frontend/src/components/IMChannelPanel.vue

@@ -208,8 +208,9 @@
 
           <div class="form-item">
             <label class="form-label">{{ $t('agentEditor.im.replyLanguage') }}</label>
-            <t-select v-model="formData.locale" :options="localeOptions" />
-            <p class="form-desc">{{ $t('agentEditor.im.replyLanguageHint') }}</p>
+            <t-select v-model="formData.language_mode" :options="languageModeOptions" />
+            <t-select v-if="formData.language_mode === 'fixed'" v-model="formData.locale" :options="localeOptions" />
+            <p class="form-desc">{{ formData.language_mode === 'follow_user' ? $t('agentEditor.im.replyLanguageFollowHint') : $t('agentEditor.im.replyLanguageHint') }}</p>
           </div>
         </section>
 
@@ -691,6 +692,11 @@ const localeOptions = computed(() => ([
   { value: 'ru-RU' as IMLocale, label: 'Русский' },
 ]));
 
+const languageModeOptions = computed(() => ([
+  { value: 'fixed', label: t('agentEditor.im.replyLanguageFixed') },
+  { value: 'follow_user', label: t('agentEditor.im.replyLanguageFollowUser') },
+]));
+
 // Feishu and Lark are the same product on separate clouds, so each has its own
 // open platform console. Bots must be created on the one matching the channel.
 const openPlatformConsole = computed(() =>
@@ -748,6 +754,7 @@ const formData = ref({
   mode: 'websocket' as 'webhook' | 'websocket' | 'longpoll',
   output_mode: 'stream' as 'stream' | 'full',
   locale: '' as IMLocale,
+  language_mode: 'fixed' as 'fixed' | 'follow_user',
   session_mode: 'user' as 'user' | 'thread',
   knowledge_base_id: '',
   credentials: defaultCredentials(),
@@ -1004,6 +1011,7 @@ async function editChannel(channel: IMChannel | IMChannelOverview) {
     mode: fullChannel.mode,
     output_mode: fullChannel.output_mode,
     locale: fullChannel.locale || '',
+    language_mode: fullChannel.language_mode || 'fixed',
     session_mode: fullChannel.session_mode || 'user',
     knowledge_base_id: fullChannel.knowledge_base_id || '',
     credentials: { ...fullChannel.credentials },
@@ -1029,6 +1037,7 @@ function resetForm() {
     mode: 'websocket',
     output_mode: 'stream',
     locale: '',
+    language_mode: 'fixed',
     session_mode: 'user',
     knowledge_base_id: '',
     credentials: defaultCredentials(),
@@ -1059,6 +1068,7 @@ async function handleSave() {
         mode: formData.value.mode,
         output_mode: formData.value.output_mode,
         locale: formData.value.locale,
+        language_mode: formData.value.language_mode,
         session_mode: formData.value.session_mode,
         knowledge_base_id: normalizeOptionalString(formData.value.knowledge_base_id),
         credentials: formData.value.credentials,
@@ -1078,6 +1088,7 @@ async function handleSave() {
         mode: formData.value.mode,
         output_mode: formData.value.output_mode,
         locale: formData.value.locale,
+        language_mode: formData.value.language_mode,
         session_mode: formData.value.session_mode,
         knowledge_base_id: normalizeOptionalString(formData.value.knowledge_base_id),
         credentials: formData.value.credentials,

frontend/src/i18n/locales/en-US.ts

@@ -8009,6 +8009,9 @@ export default {
       sessionModeThread: 'Per Thread',
       sessionModeHint: 'User mode: each person has their own conversation. Use /clear to start fresh. Thread mode: each message thread is a separate conversation. Multiple people can collaborate in the same thread.',
       replyLanguage: 'Reply Language',
+      replyLanguageFixed: 'Fixed language',
+      replyLanguageFollowUser: 'Follow the user',
+      replyLanguageFollowHint: 'Detect the language of each message. Short or unclear messages use the last detected language in this conversation, then the deployment default.',
       replyLanguageDefault: 'Use system default',
       replyLanguageHint: 'Fix the agent reply language for this channel. Leave unset to use the deployment default.',
       wechatScanBind: 'Scan to bind WeChat',

frontend/src/i18n/locales/ja-JP.ts

@@ -8009,6 +8009,9 @@ export default {
       sessionModeThread: 'スレッド単位',
       sessionModeHint: 'ユーザモード: 各ユーザが個別の会話を持ちます。/clearで新しく開始できます。スレッドモード: メッセージスレッドごとに個別の会話になります。同じスレッドで複数人が共同作業できます。',
       replyLanguage: '返信言語',
+      replyLanguageFixed: '固定言語',
+      replyLanguageFollowUser: 'ユーザーの言語に合わせる',
+      replyLanguageFollowHint: '各メッセージの言語を検出します。短文や判定不能な場合は、この会話で最後に検出された言語、次にデプロイのデフォルト言語を使用します。',
       replyLanguageDefault: 'システムのデフォルトを使用',
       replyLanguageHint: 'このチャネルでエージェントが返信する言語を固定します。未設定の場合はデプロイのデフォルト言語を使用します。',
       wechatScanBind: 'スキャンしてWeChatを連携',

frontend/src/i18n/locales/ko-KR.ts

@@ -1692,6 +1692,9 @@ export default {
       sessionModeThread: '스레드별',
       sessionModeHint: '사용자 모드: 각 사용자별 독립 대화. /clear로 새 대화 시작. 스레드 모드: 메시지 스레드별 독립 대화. 같은 스레드에서 여러 명이 함께 대화 가능.',
       replyLanguage: '응답 언어',
+      replyLanguageFixed: '고정 언어',
+      replyLanguageFollowUser: '사용자 언어 따르기',
+      replyLanguageFollowHint: '메시지마다 언어를 감지합니다. 짧거나 불분명한 메시지는 이 대화에서 마지막으로 감지한 언어를 사용하고, 없으면 배포 기본 언어를 사용합니다.',
       replyLanguageDefault: '시스템 기본값 사용',
       replyLanguageHint: '이 채널의 에이전트 응답 언어를 고정합니다. 설정하지 않으면 배포 기본 언어를 사용합니다.',
       wechatScanBind: 'QR 코드를 스캔하여 WeChat 연결',

frontend/src/i18n/locales/ru-RU.ts

@@ -1692,6 +1692,9 @@ export default {
       sessionModeThread: 'По потоку',
       sessionModeHint: 'Режим пользователя: отдельный диалог для каждого пользователя. /clear для нового диалога. Режим потока: отдельный диалог для каждого потока. Несколько человек могут общаться в одном потоке.',
       replyLanguage: 'Язык ответов',
+      replyLanguageFixed: 'Фиксированный язык',
+      replyLanguageFollowUser: 'Следовать языку пользователя',
+      replyLanguageFollowHint: 'Язык определяется для каждого сообщения. Для коротких или неясных сообщений используется последний определённый язык беседы, затем язык развёртывания по умолчанию.',
       replyLanguageDefault: 'Использовать системный язык',
       replyLanguageHint: 'Фиксирует язык ответов агента для этого канала. Если не задан, используется язык развёртывания по умолчанию.',
       wechatScanBind: 'Сканировать QR-код для привязки WeChat',

frontend/src/i18n/locales/zh-CN.ts

@@ -1694,6 +1694,9 @@ export default {
       sessionModeThread: '按话题',
       sessionModeHint: '用户模式：每个用户独立对话，使用 /clear 开始新对话。话题模式：每个消息话题独立对话，同一话题中多人可协作。',
       replyLanguage: '回复语言',
+      replyLanguageFixed: '固定语言',
+      replyLanguageFollowUser: '跟随用户语言',
+      replyLanguageFollowHint: '按消息检测回复语言。短消息或无法判断时沿用本会话上次识别的语言，再回退到部署默认语言。',
       replyLanguageDefault: '跟随系统默认语言',
       replyLanguageHint: '固定该渠道的智能体回复语言；留空时使用部署的默认语言。',
       wechatScanBind: '扫码绑定微信',

frontend/src/i18n/locales/zh-TW.ts

@@ -1694,6 +1694,9 @@ export default {
       sessionModeThread: '按話題',
       sessionModeHint: '使用者模式：每個使用者獨立對話，使用 /clear 開始新對話。話題模式：每個訊息話題獨立對話，同一話題中多人可協作。',
       replyLanguage: '回覆語言',
+      replyLanguageFixed: '固定語言',
+      replyLanguageFollowUser: '跟隨使用者語言',
+      replyLanguageFollowHint: '按訊息偵測回覆語言。短訊息或無法判斷時沿用本會話上次識別的語言，再回退到部署預設語言。',
       replyLanguageDefault: '跟隨系統預設語言',
       replyLanguageHint: '固定該通路的智慧代理回覆語言；留空時使用部署的預設語言。',
       wechatScanBind: '掃碼綁定微信',

go.mod

@@ -5,6 +5,7 @@ go 1.26.0
 require (
 	codeberg.org/readeck/go-readability/v2 v2.1.2
 	connectrpc.com/connect v1.19.1
+	github.com/abadojack/whatlanggo v1.0.1
 	github.com/DATA-DOG/go-sqlmock v1.5.2
 	github.com/JohannesKaufmann/html-to-markdown/v2 v2.5.1
 	github.com/PuerkitoBio/goquery v1.12.0

go.sum

@@ -1706,6 +1706,8 @@ github.com/VividCortex/ewma v1.2.0 h1:f58SaIzcDXrSy3kWaHNvuJgJ3Nmz59Zji6XoJR/q1o
 github.com/VividCortex/ewma v1.2.0/go.mod h1:nz4BbCtbLyFDeC9SUHbtcT5644juEuWfUAUnGx7j5l4=
 github.com/VividCortex/gohistogram v1.0.0 h1:6+hBz+qvs0JOrrNhhmR7lFxo5sINxBCGXrdtl/UvroE=
 github.com/VividCortex/gohistogram v1.0.0/go.mod h1:Pf5mBqqDxYaXu3hDrrU+w6nw50o/4+TcAqDqk/vUH7g=
+github.com/abadojack/whatlanggo v1.0.1 h1:19N6YogDnf71CTHm3Mp2qhYfkRdyvbgwWdd2EPxJRG4=
+github.com/abadojack/whatlanggo v1.0.1/go.mod h1:66WiQbSbJBIlOZMsvbKe5m6pzQovxCH9B/K8tQB2uoc=
 github.com/acarl005/stripansi v0.0.0-20180116102854-5a71ef0e047d h1:licZJFw2RwpHMqeKTCYkitsPqHNxTmd4SNR5r94FGM8=
 github.com/acarl005/stripansi v0.0.0-20180116102854-5a71ef0e047d/go.mod h1:asat636LX7Bqt5lYEZ27JNDcqxfjdBQuJ/MM4CN/Lzo=
 github.com/afex/hystrix-go v0.0.0-20180502004556-fa1af6a1f4f5 h1:rFw4nCn9iMW+Vajsk51NtYIcwSTkXr+JGrMd36kTDJw=

internal/database/im_reply_language_migration_test.go

@@ -0,0 +1,90 @@
+package database
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/golang-migrate/migrate/v4"
+	sqlite3migrate "github.com/golang-migrate/migrate/v4/database/sqlite3"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSQLiteIMReplyLanguageUpgradeAndRollback(t *testing.T) {
+	repoRoot := sqliteRepoRoot(t)
+	chdirAndRestore(t, copySQLiteMigrationsThrough(t, repoRoot, 41))
+	dbPath := filepath.Join(t.TempDir(), "im-reply-language.db")
+	opts := MigrationOptions{SQLiteDBPath: dbPath}
+	require.NoError(t, RunMigrationsWithOptions("sqlite3://unused", opts))
+	db := openSQLiteDB(t, dbPath)
+	_, err := db.Exec(`INSERT INTO sessions (id, tenant_id) VALUES ('session', 1)`)
+	require.NoError(t, err)
+	_, err = db.Exec(`INSERT INTO im_channels (id, tenant_id, agent_id, platform, name, locale)
+		VALUES ('channel', 1, 'agent', 'feishu', 'Existing channel', 'zh-CN')`)
+	require.NoError(t, err)
+	_, err = db.Exec(`INSERT INTO im_channel_sessions (id, platform, user_id, session_id, tenant_id, im_channel_id)
+		VALUES ('mapping', 'feishu', 'user', 'session', 1, 'channel')`)
+	require.NoError(t, err)
+
+	upgradeRoot := copySQLiteMigrationsThrough(t, repoRoot, 52)
+	downFile := filepath.Join("migrations", "sqlite", "000052_im_follow_user_language.down.sql")
+	downSQL, err := os.ReadFile(filepath.Join(repoRoot, downFile))
+	require.NoError(t, err)
+	require.NoError(t, os.WriteFile(filepath.Join(upgradeRoot, downFile), downSQL, 0o600))
+	chdirAndRestore(t, upgradeRoot)
+	require.NoError(t, RunMigrationsWithOptions("sqlite3://unused", opts))
+	// Repeated startup must not replay the ALTER TABLE statements.
+	require.NoError(t, RunMigrationsWithOptions("sqlite3://unused", opts))
+	version, dirty := sqliteMigrationState(t, db)
+	require.Equal(t, 52, version)
+	require.False(t, dirty)
+	var name, locale, mode, language, sessionID string
+	require.NoError(t, db.QueryRow(`SELECT name, locale, language_mode FROM im_channels
+		WHERE id = 'channel'`).Scan(&name, &locale, &mode))
+	require.Equal(t, "Existing channel", name)
+	require.Equal(t, "zh-CN", locale)
+	require.Equal(t, "fixed", mode)
+	require.NoError(t, db.QueryRow(`SELECT session_id, last_detected_language FROM im_channel_sessions
+		WHERE id = 'mapping'`).Scan(&sessionID, &language))
+	require.Equal(t, "session", sessionID)
+	require.Empty(t, language)
+	_, err = db.Exec(`UPDATE im_channels SET language_mode = 'follow_user' WHERE id = 'channel'`)
+	require.NoError(t, err)
+	require.NoError(t, db.QueryRow(`SELECT language_mode FROM im_channels
+		WHERE id = 'channel'`).Scan(&mode))
+	require.Equal(t, "follow_user", mode)
+	_, err = db.Exec(`UPDATE im_channel_sessions SET last_detected_language = 'vi' WHERE id = 'mapping'`)
+	require.NoError(t, err)
+	require.NoError(t, db.QueryRow(`SELECT last_detected_language FROM im_channel_sessions
+		WHERE id = 'mapping'`).Scan(&language))
+	require.Equal(t, "vi", language)
+
+	driver, err := sqlite3migrate.WithInstance(db, &sqlite3migrate.Config{})
+	require.NoError(t, err)
+	m, err := migrate.NewWithDatabaseInstance("file://migrations/sqlite", "sqlite3", driver)
+	require.NoError(t, err)
+	t.Cleanup(func() { _, _ = m.Close() })
+	require.NoError(t, m.Steps(-1))
+	version, dirty = sqliteMigrationState(t, db)
+	require.Equal(t, 51, version)
+	require.False(t, dirty)
+	require.False(t, sqliteColumnExists(t, db, "im_channels", "language_mode"))
+	require.False(t, sqliteColumnExists(t, db, "im_channel_sessions", "last_detected_language"))
+	require.NoError(t, db.QueryRow(`SELECT name, locale FROM im_channels
+		WHERE id = 'channel'`).Scan(&name, &locale))
+	require.Equal(t, "Existing channel", name)
+	require.Equal(t, "zh-CN", locale)
+	require.NoError(t, db.QueryRow(`SELECT session_id FROM im_channel_sessions
+		WHERE id = 'mapping'`).Scan(&sessionID))
+	require.Equal(t, "session", sessionID)
+	require.NoError(t, m.Steps(1))
+	version, dirty = sqliteMigrationState(t, db)
+	require.Equal(t, 52, version)
+	require.False(t, dirty)
+	require.NoError(t, db.QueryRow(`SELECT language_mode FROM im_channels
+		WHERE id = 'channel'`).Scan(&mode))
+	require.Equal(t, "fixed", mode)
+	require.NoError(t, db.QueryRow(`SELECT last_detected_language FROM im_channel_sessions
+		WHERE id = 'mapping'`).Scan(&language))
+	require.Empty(t, language)
+}

internal/database/migration_sqlite_versioned_schema_test.go

@@ -73,7 +73,8 @@ var versionedSQLiteColumns = map[string][]string{
 	"session_sandbox_assignments": {"released_at", "cleanup_due_at"},    // 000047
 	"tenant_invitations":          {"token", "accepted_count"},          // 000054
 	"embed_channels":              {"allow_memory"},                     // 000060
-	"im_channels":                 {"locale"},                           // 000030
+	"im_channels":                 {"locale", "language_mode"},          // 000030/052
+	"im_channel_sessions":         {"last_detected_language"},           // 000052
 	"chunks":                      {"source_locators"},                  // 000033
 	"mcp_oauth_tokens":            {"principal_type", "principal_id"},   // 000064
 	"mcp_tool_approvals":          {"enabled", "risk", "observed_risk"}, // 000091, 000126
@@ -88,7 +89,7 @@ var versionedSQLiteColumns = map[string][]string{
 	}, // 000028
 }
 
-const expectedSQLiteMigrationVersion = 51
+const expectedSQLiteMigrationVersion = 52
 
 func TestSQLiteMigrationsCreateVersionedSchema(t *testing.T) {
 	repoRoot := sqliteRepoRoot(t)

internal/handler/im.go

@@ -66,6 +66,7 @@ func (h *IMHandler) CreateIMChannel(c *gin.Context) {
 		Mode            string     `json:"mode"`
 		OutputMode      string     `json:"output_mode"`
 		Locale          string     `json:"locale"`
+		LanguageMode    string     `json:"language_mode"`
 		SessionMode     string     `json:"session_mode"`
 		KnowledgeBaseID string     `json:"knowledge_base_id"`
 		Credentials     types.JSON `json:"credentials"`
@@ -85,18 +86,24 @@ func (h *IMHandler) CreateIMChannel(c *gin.Context) {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 		return
 	}
+	languageMode, err := im.NormalizeLanguageMode(req.LanguageMode)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
 
 	channel := &im.IMChannel{
-		TenantID:    tenantID,
-		AgentID:     agentID,
-		Platform:    req.Platform,
-		Name:        req.Name,
-		Mode:        req.Mode,
-		OutputMode:  req.OutputMode,
-		Locale:      locale,
-		SessionMode: req.SessionMode,
-		Credentials: req.Credentials,
-		Enabled:     true,
+		TenantID:     tenantID,
+		AgentID:      agentID,
+		Platform:     req.Platform,
+		Name:         req.Name,
+		Mode:         req.Mode,
+		OutputMode:   req.OutputMode,
+		Locale:       locale,
+		LanguageMode: languageMode,
+		SessionMode:  req.SessionMode,
+		Credentials:  req.Credentials,
+		Enabled:      true,
 	}
 	// The route guard passes an agent it cannot find in this workspace; both
 	// the agent and the file-saving KB must belong to the channel's workspace.
@@ -226,6 +233,7 @@ func (h *IMHandler) UpdateIMChannel(c *gin.Context) {
 		Mode            *string    `json:"mode"`
 		OutputMode      *string    `json:"output_mode"`
 		Locale          *string    `json:"locale"`
+		LanguageMode    *string    `json:"language_mode"`
 		SessionMode     *string    `json:"session_mode"`
 		KnowledgeBaseID *string    `json:"knowledge_base_id"`
 		Credentials     types.JSON `json:"credentials"`
@@ -254,6 +262,14 @@ func (h *IMHandler) UpdateIMChannel(c *gin.Context) {
 		}
 		channel.Locale = locale
 	}
+	if req.LanguageMode != nil {
+		languageMode, err := im.NormalizeLanguageMode(*req.LanguageMode)
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+		channel.LanguageMode = languageMode
+	}
 	if req.SessionMode != nil {
 		channel.SessionMode = *req.SessionMode
 	}

internal/handler/im_locale_test.go

@@ -59,3 +59,23 @@ func TestCreateIMChannelRejectsUnsupportedLocale(t *testing.T) {
 		t.Fatalf("body = %s, want locale validation error", recorder.Body.String())
 	}
 }
+
+func TestCreateIMChannelRejectsInvalidLanguageMode(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	router := gin.New()
+	router.POST("/agents/:id/im-channels", NewIMHandler(nil).CreateIMChannel)
+
+	req := httptest.NewRequest(
+		http.MethodPost,
+		"/agents/agent-1/im-channels",
+		strings.NewReader(`{"platform":"feishu","language_mode":"auto"}`),
+	)
+	req.Header.Set("Content-Type", "application/json")
+	req = req.WithContext(context.WithValue(req.Context(), types.TenantIDContextKey, uint64(42)))
+	recorder := httptest.NewRecorder()
+	router.ServeHTTP(recorder, req)
+
+	if recorder.Code != http.StatusBadRequest || !strings.Contains(recorder.Body.String(), "language_mode must be") {
+		t.Fatalf("status = %d, body = %s; want language mode validation error", recorder.Code, recorder.Body.String())
+	}
+}