Add Chinese localization guidance

[lizy-coding]

Summary

This PR adds Chinese localization guidance to help Chinese-speaking users better understand how to use and contribute to the project.

Changes

• Added Chinese localization guidance
• Improved accessibility for Chinese-speaking contributors
• Clarified localized documentation usage and contribution expectations

Motivation

Chinese-speaking users may need clearer localized guidance when reading, using, or contributing to this project. This update improves documentation accessibility and lowers the barrier for participation.

Testing

• Documentation-only change
• No code changes

[gemini-code-assist]

Code Review

This pull request updates the Flutter localization guide to include workflows and examples for Chinese localization, including adding Chinese ARB files and configuring Chinese locales. The reviewer suggested keeping the Spanish locale in the example configuration to maintain consistency with other sections of the guide that still reference Spanish localization.

[gemini-code-assist]

In the Implementation Workflow section (lines 133-138), app_es.arb is still used as the primary example of adding other locales. However, Locale('es') was removed from the supportedLocales list here. To maintain consistency throughout the guide, it is better to keep Spanish in the supportedLocales list alongside the newly added Chinese locales.

Suggested change

	Locale('zh'), // Chinese
	Locale('zh', 'CN'), // Simplified Chinese, China
	Locale('es'), // Spanish
	Locale('zh'), // Chinese
	Locale('zh', 'CN'), // Simplified Chinese, China

[lizy-coding]

This is a documentation-only PR. The pending checks appear to require maintainer approval before running. Please approve them when convenient. Thanks!