[JasonYeYuhe]

Link to Issue or Description of Change

Problem:
Currently, the root README.md for Agent Development Kit (ADK) 2.0 is only available in English, creating an onboarding barrier for Chinese-speaking AI agent developers.

Solution:

• Add a complete 1:1 Simplified Chinese translation (README.zh.md) covering ADK 2.0 key features (Workflow Runtime, Task API, Modular Multi-Agent Systems, Tool Ecosystem, Code-First Development, Agent Config, Tool Confirmation HITL, Cloud Run / Gemini Enterprise Agent Platform deployment), installation with Python 3.11–3.15 constraints, Quick Start (Agent & Workflow examples, CLI & Web Dev UI, evaluation), documentation links, community repo, Vibe Coding (llms.txt), and a community translation disclaimer footer.
• Add a PyPI-safe bilingual navigation switcher in README.md using an absolute GitHub URL so links resolve cleanly on the google-adk PyPI package page.

Testing Plan

• Verified python3 scripts/check_docs.py passes with 0 errors.
• Verified mdformat --check README.md (mdformat-gfm) passes with 0 formatting issues.
• Verified codespell README.md README.zh.md and git diff --check pass with 0 warnings or trailing whitespace.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have manually tested my changes end-to-end.

[lxcxjxhx]

I read the opening section against the English README rather than the whole file, so treat this as a spot check, not a full proofread. What I checked reads well:

• Terminology keeps the English in parentheses — 代码优先（Code-First）、AI 智能体（Agents）— which is the right call for a framework README where the English terms appear in code and docs.
• Links and badges are carried over unchanged, and the "other language versions" list points at the same targets.
• The sentence structure follows Chinese rather than English word order ("助力灵活、可控地构建、评测与部署复杂 AI 智能体"), which is what makes it read as a translation rather than a transliteration.

Two things the file does not say, both about authority rather than language:

1. Which version is authoritative. A reader who lands on README.zh.md has no way to know whether it tracks README.md or has drifted. One line at the top — "本文档为 README.md 的中文翻译，如有出入以英文版为准" — costs nothing and prevents a Chinese-speaking user from filing a bug against a translated sentence that the English version never had.

2. How it stays in sync. Nothing in the PR or the repo keeps the two files together. The next English README change will make this one stale silently. That is a maintainer decision (a CI check that both files changed in the same PR is heavy for a README; a Last synced: <commit> line is cheap), but it is worth deciding now rather than after the first drift.

One structural note: README.zh.md sits next to README.md at the repo root, and the language link was added to the English file — so a Chinese reader arriving at the English README can find it. That is the right direction; the reverse link (a note at the top of the Chinese file pointing back) is the missing half.