This PR adds comprehensive French language support to the ToughRadius web interface internationalization system, resolving the request in issue #X for adding additional translation languages.

Problem

The existing internationalization system only supported Chinese (zh_CN) and English (en_US) with a basic binary toggle switch. Users requested the ability to add French translations to make the interface accessible to French-speaking administrators.

Solution

Extended the i18n system to support French (fr_FR) as a third language option with the following key changes:

Core System Enhancement

• Added FrFR = "fr_FR" language constant alongside existing ZhCN and EnUS
• Updated database initialization to create French translation buckets in BoltDB
• Enhanced language validation in SetTranslateLang() to accept French
• Extended translation file generation and cleanup operations for French support

Improved User Interface

Replaced the binary language switch with a modern dropdown selector:

Before:

<switch onLabel="中文" offLabel="English" value="{{zhlang}}">

After:

<richselect options="[
  { id: 'en_US', value: 'English' },
  { id: 'zh_CN', value: '中文' },
  { id: 'fr_FR', value: 'Français' }
]">

Enhanced Language Switching

Updated the controller endpoint from a binary parameter to accept language codes:

• /admin/translate/switch/fr_FR - Switch to French
• /admin/translate/switch/zh_CN - Switch to Chinese
• /admin/translate/switch/en_US - Switch to English
• Maintains backward compatibility with existing binary URLs (/switch/1 and /switch/0)

Translation Management

• Added French option to the admin translation interface
• Enabled bulk import/export for French translation files
• Extended auto-translation features to support French

Usage

Administrators can now:

1. Select "Français" from the language dropdown in the main interface
2. Create French translations through the admin panel by selecting "fr_FR" as the language
3. Import existing French translation JSON files
4. Use the "Translate All" feature to automatically generate French translations

Backward Compatibility

All existing functionality is preserved:

• Current Chinese and English translations remain unchanged
• Legacy binary language switch URLs continue to work
• No breaking changes to existing API endpoints or database structure
• All template variables maintain consistency

Testing

• ✅ Go build compiles successfully with new language support
• ✅ Unit tests pass for translation functionality
• ✅ Database operations validated for French translation storage
• ✅ Language switching mechanism tested across all three languages

This implementation provides a solid foundation for French localization while maintaining the system's existing stability and functionality.

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