diff --git a/packages/core/src/PageAgentCore.ts b/packages/core/src/PageAgentCore.ts
index e6d8c66..ee38e47 100644
--- a/packages/core/src/PageAgentCore.ts
+++ b/packages/core/src/PageAgentCore.ts
@@ -417,10 +417,8 @@ export class PageAgentCore extends EventTarget {
 			return this.config.customSystemPrompt
 		}
 
-		let systemPrompt = SYSTEM_PROMPT
-
 		const targetLanguage = this.config.language === 'zh-CN' ? '中文' : 'English'
-		systemPrompt = systemPrompt.replace(
+		const systemPrompt = SYSTEM_PROMPT.replace(
 			/Default working language: \*\*.*?\*\*/,
 			`Default working language: **${targetLanguage}**`
 		)
diff --git a/packages/core/src/prompts/system_prompt.md b/packages/core/src/prompts/system_prompt.md
index d20571e..71b1882 100644
--- a/packages/core/src/prompts/system_prompt.md
+++ b/packages/core/src/prompts/system_prompt.md
@@ -10,7 +10,7 @@ You excel at following tasks:
 </intro>
 
 <language_settings>
-- Default working language: **中文**
+- Default working language: **English**
 - Use the language that user is using. Return in user's language.
 </language_settings>
 
diff --git a/packages/extension/src/agent/MultiPageAgent.ts b/packages/extension/src/agent/MultiPageAgent.ts
index f53461e..9076d90 100644
--- a/packages/extension/src/agent/MultiPageAgent.ts
+++ b/packages/extension/src/agent/MultiPageAgent.ts
@@ -12,10 +12,18 @@ import { createTabTools } from './tabTools'
  */
 export class MultiPageAgent extends PageAgentCore {
 	constructor(config: Omit<PageAgentConfig, 'pageController'>) {
+		// multi page controller
 		const tabsController = new TabsController()
 		const pageController = new RemotePageController(tabsController)
 		const customTools = createTabTools(tabsController)
 
+		// system prompt
+		const targetLanguage = config.language === 'zh-CN' ? '中文' : 'English'
+		const systemPrompt = SYSTEM_PROMPT.replace(
+			/Default working language: \*\*.*?\*\*/,
+			`Default working language: **${targetLanguage}**`
+		)
+
 		/**
 		 * When the agent is in side-panel and user closed the side-panel.
 		 * There is no chance for isAgentRunning to be set false.
@@ -29,7 +37,7 @@ export class MultiPageAgent extends PageAgentCore {
 			...config,
 			pageController: pageController as any,
 			customTools: customTools,
-			customSystemPrompt: SYSTEM_PROMPT,
+			customSystemPrompt: systemPrompt,
 
 			onBeforeTask: async (agent) => {
 				await tabsController.init(agent.task)
diff --git a/packages/extension/src/agent/system_prompt.md b/packages/extension/src/agent/system_prompt.md
index 6784b2a..7831d37 100644
--- a/packages/extension/src/agent/system_prompt.md
+++ b/packages/extension/src/agent/system_prompt.md
@@ -10,7 +10,7 @@ You excel at following tasks:
 </intro>
 
 <language_settings>
-- Default working language: **中文**
+- Default working language: **English**
 - Use the language that user is using. Return in user's language.
 </language_settings>