Add i18n support for German, Ukrainian, Russian, and Japanese languages

Description

This PR adds internationalization (i18n) support for four additional languages:German (de),Ukrainian (uk),Russian (ru), andJapanese (ja). The changes include complete translation files for all UI components and updates to the i18n configuration to make these languages available in the language selector.

Related Issues

N/A - This is a feature addition to expand language support for the LightRAG WebUI interface.

Changes Made

• Added four new translation files:

  • lightrag_webui/src/locales/de.json - Complete German translations (465 lines)
  • lightrag_webui/src/locales/uk.json - Complete Ukrainian translations (465 lines)
  • lightrag_webui/src/locales/ru.json - Complete Russian translations (465 lines)
  • lightrag_webui/src/locales/ja.json - Complete Japanese translations (465 lines)

• Updated i18n configuration files:

  • lightrag_webui/src/i18n.ts - Added imports for new locale files and registered them in i18next resources
  • lightrag_webui/src/stores/settings.ts - Extended Language type union to include'de' | 'uk' | 'ru' | 'ja'
  • lightrag_webui/src/components/AppSettings.tsx - Added language selector options with native language names (Deutsch, Українська, Русский, 日本語)

All translation files follow the same structure as existing locales (en, zh, fr, ar, zh_TW) and provide complete translations for:

• Settings panel (language, theme options)
• Header navigation (documents, knowledge graph, retrieval, API)
• Login interface and authentication messages
• Document management panel (upload, delete, clear operations)
• Knowledge graph visualization (node types, properties, search)
• Retrieval/query interface (query modes, parameters, chat messages)
• API documentation page
• Common UI elements (buttons, pagination, error messages)

Checklist

• Changes tested locally
• Code reviewed
• Documentation updated (if necessary)
• Unit tests added (if applicable)

Additional Notes

• All translation files contain 465 lines matching the exact structure of existing locale files
• Languages are added in the order: German, Ukrainian, Russian, Japanese
• The language selector dropdown now displays native language names: Deutsch, Українська, Русский, 日本語
• No breaking changes introduced - this is a pure addition of new language support
• Translations cover all UI components and user-facing strings throughout the application
• The implementation follows the existing i18n pattern used for other languages in the project