diff --git a/backend/app/api/graph.py b/backend/app/api/graph.py
index bcd6c5f..759ff48 100644
--- a/backend/app/api/graph.py
+++ b/backend/app/api/graph.py
@@ -15,7 +15,7 @@ from ..services.graph_builder import GraphBuilderService
 from ..services.text_processor import TextProcessor
 from ..utils.file_parser import FileParser
 from ..utils.logger import get_logger
-from ..utils.locale import t
+from ..utils.locale import t, get_locale, set_locale
 from ..models.task import TaskManager, TaskStatus
 from ..models.project import ProjectManager, ProjectStatus
 
@@ -371,8 +371,12 @@ def build_graph():
         project.graph_build_task_id = task_id
         ProjectManager.save_project(project)
         
+        # Capture locale before spawning background thread
+        current_locale = get_locale()
+
         # 启动后台任务
         def build_task():
+            set_locale(current_locale)
             build_logger = get_logger('mirofish.build')
             try:
                 build_logger.info(f"[{task_id}] 开始构建图谱...")
diff --git a/backend/app/api/report.py b/backend/app/api/report.py
index f803f1f..d7f2a4d 100644
--- a/backend/app/api/report.py
+++ b/backend/app/api/report.py
@@ -15,7 +15,7 @@ from ..services.simulation_manager import SimulationManager
 from ..models.project import ProjectManager
 from ..models.task import TaskManager, TaskStatus
 from ..utils.logger import get_logger
-from ..utils.locale import t
+from ..utils.locale import t, get_locale, set_locale
 
 logger = get_logger('mirofish.api.report')
 
@@ -121,8 +121,12 @@ def generate_report():
             }
         )
         
+        # Capture locale before spawning background thread
+        current_locale = get_locale()
+
         # 定义后台任务
         def run_generate():
+            set_locale(current_locale)
             try:
                 task_manager.update_task(
                     task_id,
diff --git a/backend/app/api/simulation.py b/backend/app/api/simulation.py
index 2535f13..2c1b6b1 100644
--- a/backend/app/api/simulation.py
+++ b/backend/app/api/simulation.py
@@ -14,7 +14,7 @@ from ..services.oasis_profile_generator import OasisProfileGenerator
 from ..services.simulation_manager import SimulationManager, SimulationStatus
 from ..services.simulation_runner import SimulationRunner, RunnerStatus
 from ..utils.logger import get_logger
-from ..utils.locale import t
+from ..utils.locale import t, get_locale, set_locale
 from ..models.project import ProjectManager
 
 logger = get_logger('mirofish.api.simulation')
@@ -501,8 +501,12 @@ def prepare_simulation():
         state.status = SimulationStatus.PREPARING
         manager._save_simulation_state(state)
         
+        # Capture locale before spawning background thread
+        current_locale = get_locale()
+
         # 定义后台任务
         def run_prepare():
+            set_locale(current_locale)
             try:
                 task_manager.update_task(
                     task_id,
diff --git a/backend/app/services/graph_builder.py b/backend/app/services/graph_builder.py
index d642451..37c9969 100644
--- a/backend/app/services/graph_builder.py
+++ b/backend/app/services/graph_builder.py
@@ -17,7 +17,7 @@ from ..config import Config
 from ..models.task import TaskManager, TaskStatus
 from ..utils.zep_paging import fetch_all_nodes, fetch_all_edges
 from .text_processor import TextProcessor
-from ..utils.locale import t
+from ..utils.locale import t, get_locale, set_locale
 
 
 @dataclass
@@ -84,10 +84,13 @@ class GraphBuilderService:
             }
         )
         
+        # Capture locale before spawning background thread
+        current_locale = get_locale()
+
         # 在后台线程中执行构建
         thread = threading.Thread(
             target=self._build_graph_worker,
-            args=(task_id, text, ontology, graph_name, chunk_size, chunk_overlap, batch_size)
+            args=(task_id, text, ontology, graph_name, chunk_size, chunk_overlap, batch_size, current_locale)
         )
         thread.daemon = True
         thread.start()
@@ -102,9 +105,11 @@ class GraphBuilderService:
         graph_name: str,
         chunk_size: int,
         chunk_overlap: int,
-        batch_size: int
+        batch_size: int,
+        locale: str = 'zh'
     ):
         """图谱构建工作线程"""
+        set_locale(locale)
         try:
             self.task_manager.update_task(
                 task_id,
diff --git a/backend/app/services/oasis_profile_generator.py b/backend/app/services/oasis_profile_generator.py
index 83f49cb..0c1d6ec 100644
--- a/backend/app/services/oasis_profile_generator.py
+++ b/backend/app/services/oasis_profile_generator.py
@@ -20,7 +20,7 @@ from zep_cloud.client import Zep
 
 from ..config import Config
 from ..utils.logger import get_logger
-from ..utils.locale import get_language_instruction, t
+from ..utils.locale import get_language_instruction, get_locale, set_locale, t
 from .zep_entity_reader import EntityNode, ZepEntityReader
 
 logger = get_logger('mirofish.oasis_profile')
@@ -916,8 +916,12 @@ class OasisProfileGenerator:
                 except Exception as e:
                     logger.warning(f"实时保存 profiles 失败: {e}")
         
+        # Capture locale before spawning thread pool workers
+        current_locale = get_locale()
+
         def generate_single_profile(idx: int, entity: EntityNode) -> tuple:
             """生成单个profile的工作函数"""
+            set_locale(current_locale)
             entity_type = entity.get_entity_type() or "Entity"
             
             try:
diff --git a/backend/app/services/simulation_runner.py b/backend/app/services/simulation_runner.py
index 8c35380..e86021f 100644
--- a/backend/app/services/simulation_runner.py
+++ b/backend/app/services/simulation_runner.py
@@ -20,6 +20,7 @@ from queue import Queue
 
 from ..config import Config
 from ..utils.logger import get_logger
+from ..utils.locale import get_locale, set_locale
 from .zep_graph_memory_updater import ZepGraphMemoryManager
 from .simulation_ipc import SimulationIPCClient, CommandType, IPCResponse
 
@@ -455,10 +456,13 @@ class SimulationRunner:
             cls._processes[simulation_id] = process
             cls._save_run_state(state)
             
+            # Capture locale before spawning monitor thread
+            current_locale = get_locale()
+
             # 启动监控线程
             monitor_thread = threading.Thread(
                 target=cls._monitor_simulation,
-                args=(simulation_id,),
+                args=(simulation_id, current_locale),
                 daemon=True
             )
             monitor_thread.start()
@@ -475,8 +479,9 @@ class SimulationRunner:
         return state
     
     @classmethod
-    def _monitor_simulation(cls, simulation_id: str):
+    def _monitor_simulation(cls, simulation_id: str, locale: str = 'zh'):
         """监控模拟进程，解析动作日志"""
+        set_locale(locale)
         sim_dir = os.path.join(cls.RUN_STATE_DIR, simulation_id)
         
         # 新的日志结构：分平台的动作日志
diff --git a/backend/app/services/zep_graph_memory_updater.py b/backend/app/services/zep_graph_memory_updater.py
index a8f3cec..e034fee 100644
--- a/backend/app/services/zep_graph_memory_updater.py
+++ b/backend/app/services/zep_graph_memory_updater.py
@@ -16,6 +16,7 @@ from zep_cloud.client import Zep
 
 from ..config import Config
 from ..utils.logger import get_logger
+from ..utils.locale import get_locale, set_locale
 
 logger = get_logger('mirofish.zep_graph_memory_updater')
 
@@ -275,10 +276,14 @@ class ZepGraphMemoryUpdater:
         """启动后台工作线程"""
         if self._running:
             return
-        
+
+        # Capture locale before spawning background thread
+        current_locale = get_locale()
+
         self._running = True
         self._worker_thread = threading.Thread(
             target=self._worker_loop,
+            args=(current_locale,),
             daemon=True,
             name=f"ZepMemoryUpdater-{self.graph_id[:8]}"
         )
@@ -356,8 +361,9 @@ class ZepGraphMemoryUpdater:
         
         self.add_activity(activity)
     
-    def _worker_loop(self):
+    def _worker_loop(self, locale: str = 'zh'):
         """后台工作循环 - 按平台批量发送活动到Zep"""
+        set_locale(locale)
         while self._running or not self._activity_queue.empty():
             try:
                 # 尝试从队列获取活动（超时1秒）
diff --git a/backend/app/utils/__init__.py b/backend/app/utils/__init__.py
index e022abb..e70161a 100644
--- a/backend/app/utils/__init__.py
+++ b/backend/app/utils/__init__.py
@@ -4,7 +4,7 @@
 
 from .file_parser import FileParser
 from .llm_client import LLMClient
-from .locale import t, get_locale, get_language_instruction
+from .locale import t, get_locale, set_locale, get_language_instruction
 
-__all__ = ['FileParser', 'LLMClient', 't', 'get_locale', 'get_language_instruction']
+__all__ = ['FileParser', 'LLMClient', 't', 'get_locale', 'set_locale', 'get_language_instruction']
 
diff --git a/backend/app/utils/locale.py b/backend/app/utils/locale.py
index 8da76c7..868c4f0 100644
--- a/backend/app/utils/locale.py
+++ b/backend/app/utils/locale.py
@@ -1,7 +1,10 @@
 import json
 import os
+import threading
 from flask import request, has_request_context
 
+_thread_local = threading.local()
+
 _locales_dir = os.path.join(os.path.dirname(__file__), '..', '..', '..', 'locales')
 
 # Load language registry
@@ -17,10 +20,15 @@ for filename in os.listdir(_locales_dir):
             _translations[locale_name] = json.load(f)
 
 
+def set_locale(locale: str):
+    """Set locale for current thread. Call at the start of background threads."""
+    _thread_local.locale = locale
+
+
 def get_locale() -> str:
     if has_request_context():
         return request.headers.get('Accept-Language', 'zh')
-    return 'zh'
+    return getattr(_thread_local, 'locale', 'zh')
 
 
 def t(key: str, **kwargs) -> str: