feat(i18n): add Simplified Chinese localization

[AstronW]

Type of Change

• Feature

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Pre-Submission Checklist

• No existing Pull Request for this change
• Descriptive commit message
• Self-reviewed the code
• Comments added where necessary
• No new warnings or errors introduced
• Changes made in a separate branch
• Branch named using prefix (e.g., bug/, feat/, clean/, release/)
• All user-facing text supports localization (if applicable)
• Updated documentation or relevant README sections (if applicable)
• Added screenshots or demo for UI changes (if applicable)

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Before Submitting Your Pull Request

• Clear and descriptive PR title
• Detailed summary of the changes made
• Linked relevant issue(s) using Closes #XXXX or Fixes #XXXX (if applicable)

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Summary of Changes

Adds Simplified Chinese localization support.

Key Changes

1. Added Simplified Chinese app strings and language names.
2. Registered Chinese in the language list and locale constants.
3. Updated README translation list to include Chinese.

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Test Information

• MultiLauncher Version: current main
• Device Name: Pixel 8 AVD
• Android Version: Android 17
• Other Notes: