[JasonYeYuhe]

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Link to Issue or Description of Change

2. Or, if no issue exists, describe the change:

Problem:
Developers and enterprise engineers in the Chinese-speaking community looking to use Google's Agent Development Kit (ADK) in Java lack a native-language reference for understanding the framework's key features, Maven dependencies, code-first architecture, and A2A integration.

Solution:
Introduce a faithful and standardized Simplified Chinese translation (README.zh.md) and add a PyPI/Maven-safe bidirectional language switcher navigation link in README.md.

Testing Plan

This is a documentation-only PR:

• Verified all hyperlinks, Maven artifact coordinates, sample Java code snippets, and image URLs.
• Verified formatting using git diff --check with zero trailing whitespace.
• Verified single commit and conventional commit title format for repository CI requirements.

Checklist

• I have read the CONTRIBUTING.md document.
• My pull request contains a single commit.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

• PyPI / Maven / GitHub safe absolute links are used in README.md.
• Single source of truth translation disclaimer added to the footer of README.zh.md.