add language change

Author: flyingcys

docs/en/index.rst

@@ -9,6 +9,8 @@ TuyaOpen Development Guide
 
 .. figure:: ../images/TuyaOpen.png
 
+`[中文] <https://docs.tuyaopen.io/zh>`_ | [English]
+
 This open-source framework for AIoT development, built on the proven TuyaOS IoT system, delivers cross-platform architecture, component-based design, and enterprise-grade security validated by 100M+ global devices. Its on-device AI inference engine with cloud-edge multimodal AI capabilities enables developers to access compliant Chinese LLMs (DeepSeek/Qwen/Doubao) or integrate global AI services (ChatGPT/Claude/Gemini) through unified API toolkits for text/voice interactions and image/video generation.
 
 Supporting mainstream open-source ecosystems, it allows seamless porting across chipsets/development boards, accelerating prototyping to production-ready deployment within 72 hours via Tuya's certified hardware partners.

docs/zh/index.rst

@@ -9,6 +9,8 @@ TuyaOpen 开发指南
 
 .. figure:: ../images/TuyaOpen.png
 
+[中文] | `[English] <https://docs.tuyaopen.io/en>`_
+
 TuyaOpen 是一个面向 AIoT 行业的开源、开放的开发框架，基于成熟的商业级 IoT 系统 TuyaOS 构建而成。它继承了跨平台、跨系统、组件化和安全合规等核心特性，并经过全球亿级设备和百万级用户的验证。
 
 TuyaOpen 集成了端侧 AI 推理引擎，支持涂鸦云智能体中枢，支持端云融合的多模态 AI 能力。开发者可以无缝调用国内合规的大模型（如 DeepSeek、千问、豆包）或灵活对接全球顶尖的 AI 服务（如 ChatGPT、Claude、Gemini）。通过多样化的工具生态，开发者能够实现文字和语音对话、图片生成、视频生成等多种 AI 功能。