Locale and translations for "System Settings" App

[GT-610]

This PR completes the translation work for System Settings across all supported languages (Simplified Chinese, Traditional Chinese (HK and TW), Japanese and Korean). HTML layout has also been optimized to match the locale needs.

404 page has been localized as well and I also did some minor tweaks for existing translations.

However, I've noticed a new issue: Using applocale.js cause too much performance decrease, and if nested pages use applocale.js it will cause too many requests on it, and some browsers might fail to load the JS prooperly, and locales will not show as a result.

Additionally, I propose a potential migration of locale rendering from the JS frontend to the Go backend. Rendering HTML and serving it directly will definately solve the issue, but it might comsume a little bit more on the server side. Further performance validation is required before finalizing this change.

Details

• Translation Completion:
  • Fully translated "System Settings" content into all supported languages.
  • Ensured consistency and accuracy in translations by cross-referencing with localization guidelines.

Next Steps

• Conduct performance tests to validate the efficiency of backend-based locale rendering.
• Gather feedback on the proposed migration strategy and make adjustments as necessary.
• Finalize implementation based on test results and stakeholder input.

[tobychui]

Generally looks ok, will merge into the dev branch and test it over there.