fix(i18n): use WEKNORA_LANGUAGE env for prompt language fallback instead of hardcoded zh-CN

- Add DefaultLanguage() that reads WEKNORA_LANGUAGE env with zh-CN fallback
- Replace hardcoded zh-CN in LanguageNameFromContext with DefaultLanguage()
- Unify middleware/language.go to use types.DefaultLanguage()
- Add Language field to DocumentProcessPayload (8 enqueue sites + worker restore)
- Add Language field to ImageMultimodalPayload (enqueue + worker restore)
- Propagate language from ImageMultimodalPayload to QuestionGenerationPayload

internal/application/service/image_multimodal.go

@@ -79,6 +79,9 @@ func (s *ImageMultimodalService) Handle(ctx context.Context, task *asynq.Task) e
 		payload.ChunkID, payload.ImageURL, payload.EnableOCR, payload.EnableCaption)
 
 	ctx = context.WithValue(ctx, types.TenantIDContextKey, payload.TenantID)
+	if payload.Language != "" {
+		ctx = context.WithValue(ctx, types.LanguageContextKey, payload.Language)
+	}
 
 	vlmModel, err := s.resolveVLM(ctx, payload.KnowledgeBaseID)
 	if err != nil {
@@ -437,6 +440,7 @@ func (s *ImageMultimodalService) enqueueQuestionGenerationIfEnabled(ctx context.
 		KnowledgeBaseID: payload.KnowledgeBaseID,
 		KnowledgeID:     payload.KnowledgeID,
 		QuestionCount:   questionCount,
+		Language:        payload.Language,
 	}
 	payloadBytes, err := json.Marshal(taskPayload)
 	if err != nil {

internal/application/service/knowledge.go

@@ -383,6 +383,7 @@ func (s *knowledgeService) CreateKnowledgeFromFile(ctx context.Context,
 		}
 	}
 
+	lang, _ := types.LanguageFromContext(ctx)
 	taskPayload := types.DocumentProcessPayload{
 		TenantID:                 tenantID,
 		KnowledgeID:              knowledge.ID,
@@ -393,6 +394,7 @@ func (s *knowledgeService) CreateKnowledgeFromFile(ctx context.Context,
 		EnableMultimodel:         enableMultimodelValue,
 		EnableQuestionGeneration: enableQuestionGeneration,
 		QuestionCount:            questionCount,
+		Language:                 lang,
 	}
 
 	payloadBytes, err := json.Marshal(taskPayload)
@@ -557,6 +559,7 @@ func (s *knowledgeService) CreateKnowledgeFromURL(ctx context.Context,
 		}
 	}
 
+	lang, _ := types.LanguageFromContext(ctx)
 	taskPayload := types.DocumentProcessPayload{
 		TenantID:                 tenantID,
 		KnowledgeID:              knowledge.ID,
@@ -565,6 +568,7 @@ func (s *knowledgeService) CreateKnowledgeFromURL(ctx context.Context,
 		EnableMultimodel:         enableMultimodelValue,
 		EnableQuestionGeneration: enableQuestionGeneration,
 		QuestionCount:            questionCount,
+		Language:                 lang,
 	}
 
 	payloadBytes, err := json.Marshal(taskPayload)
@@ -770,6 +774,7 @@ func (s *knowledgeService) createKnowledgeFromFileURL(
 		}
 	}
 
+	lang, _ := types.LanguageFromContext(ctx)
 	taskPayload := types.DocumentProcessPayload{
 		TenantID:                 tenantID,
 		KnowledgeID:              knowledge.ID,
@@ -780,6 +785,7 @@ func (s *knowledgeService) createKnowledgeFromFileURL(
 		EnableMultimodel:         enableMultimodelValue,
 		EnableQuestionGeneration: enableQuestionGeneration,
 		QuestionCount:            questionCount,
+		Language:                 lang,
 	}
 
 	payloadBytes, err := json.Marshal(taskPayload)
@@ -988,6 +994,7 @@ func (s *knowledgeService) createKnowledgeFromPassageInternal(ctx context.Contex
 			}
 		}
 
+		lang, _ := types.LanguageFromContext(ctx)
 		taskPayload := types.DocumentProcessPayload{
 			TenantID:                 tenantID,
 			KnowledgeID:              knowledge.ID,
@@ -996,6 +1003,7 @@ func (s *knowledgeService) createKnowledgeFromPassageInternal(ctx context.Contex
 			EnableMultimodel:         false, // 文本段落不支持多模态
 			EnableQuestionGeneration: enableQuestionGeneration,
 			QuestionCount:            questionCount,
+			Language:                 lang,
 		}
 
 		payloadBytes, err := json.Marshal(taskPayload)
@@ -2704,6 +2712,7 @@ func (s *knowledgeService) ReparseKnowledge(ctx context.Context, knowledgeID str
 			}
 		}
 
+		lang, _ := types.LanguageFromContext(ctx)
 		taskPayload := types.DocumentProcessPayload{
 			TenantID:                 tenantID,
 			KnowledgeID:              existing.ID,
@@ -2714,6 +2723,7 @@ func (s *knowledgeService) ReparseKnowledge(ctx context.Context, knowledgeID str
 			EnableMultimodel:         enableMultimodel,
 			EnableQuestionGeneration: enableQuestionGeneration,
 			QuestionCount:            questionCount,
+			Language:                 lang,
 		}
 
 		payloadBytes, err := json.Marshal(taskPayload)
@@ -2754,6 +2764,7 @@ func (s *knowledgeService) ReparseKnowledge(ctx context.Context, knowledgeID str
 			}
 		}
 
+		lang, _ := types.LanguageFromContext(ctx)
 		taskPayload := types.DocumentProcessPayload{
 			TenantID:                 tenantID,
 			KnowledgeID:              existing.ID,
@@ -2764,6 +2775,7 @@ func (s *knowledgeService) ReparseKnowledge(ctx context.Context, knowledgeID str
 			EnableMultimodel:         enableMultimodel,
 			EnableQuestionGeneration: enableQuestionGeneration,
 			QuestionCount:            questionCount,
+			Language:                 lang,
 		}
 
 		payloadBytes, err := json.Marshal(taskPayload)
@@ -2799,6 +2811,7 @@ func (s *knowledgeService) ReparseKnowledge(ctx context.Context, knowledgeID str
 			}
 		}
 
+		lang, _ := types.LanguageFromContext(ctx)
 		taskPayload := types.DocumentProcessPayload{
 			TenantID:                 tenantID,
 			KnowledgeID:              existing.ID,
@@ -2807,6 +2820,7 @@ func (s *knowledgeService) ReparseKnowledge(ctx context.Context, knowledgeID str
 			EnableMultimodel:         enableMultimodel,
 			EnableQuestionGeneration: enableQuestionGeneration,
 			QuestionCount:            questionCount,
+			Language:                 lang,
 		}
 
 		payloadBytes, err := json.Marshal(taskPayload)
@@ -7380,6 +7394,9 @@ func (s *knowledgeService) ProcessDocument(ctx context.Context, t *asynq.Task) e
 	ctx = logger.WithRequestID(ctx, payload.RequestId)
 	ctx = logger.WithField(ctx, "document_process", payload.KnowledgeID)
 	ctx = context.WithValue(ctx, types.TenantIDContextKey, payload.TenantID)
+	if payload.Language != "" {
+		ctx = context.WithValue(ctx, types.LanguageContextKey, payload.Language)
+	}
 
 	// 获取任务重试信息，用于判断是否是最后一次重试
 	retryCount, _ := asynq.GetRetryCount(ctx)
@@ -7826,6 +7843,7 @@ func (s *knowledgeService) enqueueImageMultimodalTasks(
 			chunkID = chunks[0].ChunkID
 		}
 
+		lang, _ := types.LanguageFromContext(ctx)
 		payload := types.ImageMultimodalPayload{
 			TenantID:        knowledge.TenantID,
 			KnowledgeID:     knowledge.ID,
@@ -7834,6 +7852,7 @@ func (s *knowledgeService) enqueueImageMultimodalTasks(
 			ImageURL:        img.ServingURL,
 			EnableOCR:       true,
 			EnableCaption:   true,
+			Language:        lang,
 		}
 
 		payloadBytes, err := json.Marshal(payload)
@@ -9026,6 +9045,7 @@ func (s *knowledgeService) moveKnowledgeReparse(
 			}
 		}
 
+		lang, _ := types.LanguageFromContext(ctx)
 		taskPayload := types.DocumentProcessPayload{
 			TenantID:                 tenantID,
 			KnowledgeID:              knowledge.ID,
@@ -9036,6 +9056,7 @@ func (s *knowledgeService) moveKnowledgeReparse(
 			EnableMultimodel:         enableMultimodel,
 			EnableQuestionGeneration: enableQuestionGeneration,
 			QuestionCount:            questionCount,
+			Language:                 lang,
 		}
 
 		payloadBytes, err := json.Marshal(taskPayload)

internal/middleware/language.go

@@ -2,43 +2,46 @@ package middleware
 
 import (
 	"context"
-	"os"
 	"strings"
 
 	"github.com/Tencent/WeKnora/internal/types"
 	"github.com/gin-gonic/gin"
 )
 
-// DefaultLanguage is the fallback language when no preference is specified.
-const DefaultLanguage = "zh-CN"
-
 // Language extracts the user's language preference and injects it into the request context.
 //
 // Priority (highest to lowest):
-//  1. Accept-Language HTTP header (first tag, e.g. "zh-CN,zh;q=0.9" → "zh-CN")
-//  2. WEKNORA_LANGUAGE environment variable
-//  3. DefaultLanguage ("zh-CN")
+//  1. WEKNORA_LANGUAGE environment variable (deployment-level override for document processing language)
+//  2. Accept-Language HTTP header (first tag, e.g. "zh-CN,zh;q=0.9" → "zh-CN")
+//  3. "zh-CN" hardcoded fallback
+//
+// WEKNORA_LANGUAGE takes precedence over Accept-Language because the UI locale (menu language)
+// and the document processing language (question/summary generation) are separate concerns.
+// A user may prefer English UI while processing Korean documents.
 func Language() gin.HandlerFunc {
-	// Read env var once at startup
-	envLang := strings.TrimSpace(os.Getenv("WEKNORA_LANGUAGE"))
+	// Read env var once at startup; empty string means "not configured"
+	envLang := types.EnvLanguage()
 
 	return func(c *gin.Context) {
+		// 1. WEKNORA_LANGUAGE env takes precedence (deployment-level document language)
+		if envLang != "" {
+			c.Set(types.LanguageContextKey.String(), envLang)
+			ctx := context.WithValue(c.Request.Context(), types.LanguageContextKey, envLang)
+			c.Request = c.Request.WithContext(ctx)
+			c.Next()
+			return
+		}
+
 		lang := ""
 
-		// 1. Try Accept-Language header
+		// 2. Try Accept-Language header
 		if acceptLang := c.GetHeader("Accept-Language"); acceptLang != "" {
-			// Parse the first language tag (e.g. "zh-CN,zh;q=0.9,en;q=0.8" → "zh-CN")
 			lang = parseFirstLanguageTag(acceptLang)
 		}
 
-		// 2. Fallback to environment variable
-		if lang == "" && envLang != "" {
-			lang = envLang
-		}
-
-		// 3. Fallback to default
+		// 3. Fallback to hardcoded default
 		if lang == "" {
-			lang = DefaultLanguage
+			lang = "zh-CN"
 		}
 
 		// Inject into context

internal/types/context_helpers.go

@@ -1,6 +1,24 @@
 package types
 
-import "context"
+import (
+	"context"
+	"os"
+	"strings"
+)
+
+// EnvLanguage returns the WEKNORA_LANGUAGE environment variable value, or empty string if unset.
+func EnvLanguage() string {
+	return strings.TrimSpace(os.Getenv("WEKNORA_LANGUAGE"))
+}
+
+// DefaultLanguage returns the configured default language locale.
+// It reads the WEKNORA_LANGUAGE environment variable; if unset, falls back to "zh-CN".
+func DefaultLanguage() string {
+	if lang := EnvLanguage(); lang != "" {
+		return lang
+	}
+	return "zh-CN"
+}
 
 // TenantIDFromContext extracts the tenant ID from ctx.
 // Returns (0, false) when the key is absent or the value is not uint64.
@@ -55,10 +73,11 @@ func LanguageFromContext(ctx context.Context) (string, bool) {
 
 // LanguageNameFromContext returns the human-readable language name for use in prompts.
 // e.g. "zh-CN" -> "Chinese (Simplified)", "en-US" -> "English", "ko-KR" -> "Korean"
+// Falls back to DefaultLanguage() (WEKNORA_LANGUAGE env, then "zh-CN").
 func LanguageNameFromContext(ctx context.Context) string {
 	lang, ok := LanguageFromContext(ctx)
 	if !ok {
-		lang = "zh-CN"
+		lang = DefaultLanguage()
 	}
 	return LanguageLocaleName(lang)
 }

internal/types/extract_graph.go

@@ -39,6 +39,7 @@ type DocumentProcessPayload struct {
 	EnableMultimodel         bool     `json:"enable_multimodel"`
 	EnableQuestionGeneration bool     `json:"enable_question_generation"` // 是否启用问题生成
 	QuestionCount            int      `json:"question_count,omitempty"`   // 每个chunk生成的问题数量
+	Language                 string   `json:"language,omitempty"`         // Request locale for {{language}} in prompt templates
 }
 
 // FAQImportPayload represents the FAQ import task payload (including dry run mode)
@@ -151,6 +152,7 @@ type ImageMultimodalPayload struct {
 	ImageLocalPath  string `json:"image_local_path"`   // deprecated: kept for backward compat with in-flight tasks
 	EnableOCR       bool   `json:"enable_ocr"`
 	EnableCaption   bool   `json:"enable_caption"`
+	Language        string `json:"language,omitempty"` // Request locale for {{language}} in prompt templates
 }
 
 // KBCloneTaskStatus represents the status of a knowledge base clone task