[Feature]: Add Chinese (Simplified & Traditional) localization support

[shuo1104]

Is there an existing feature request for this?

• I have searched the existing issues

Problem or Motivation

Currently, the application UI is only available in English. Adding localization for Simplified Chinese (zh-Hans) and Traditional Chinese (zh-Hant) will significantly improve the user experience for Chinese-speaking users and help broaden the app's user base.

Proposed Solution

Add Chinese (Simplified and Traditional) localization support to the macOS app.

Requirements:

• Extract hardcoded strings from SwiftUI views, navigation bars, player controls, sidebar, and settings into Localizable.xcstrings (or Localizable.strings).
• Create localization files for Simplified Chinese (zh-Hans) and Traditional Chinese (zh-Hant).
• Translate all key UI components (Player bar, Sidebar playlists, Settings, Search placeholders, and Empty states) accurately into both Chinese variants.
• Ensure dynamic layout elements adapt cleanly without UI clipping or text truncation when language changes.
• Follow SwiftUI best practices using LocalizedStringKey or standard Text() localization APIs.

Alternatives Considered

No response

Feature Area

UI / Visual

How important is this feature to you?

Essential for my use case

Mockups or Examples

No response

Additional Context

No response