feat: backend i18n

[Calcium-Ion]

Summary by CodeRabbit

Release Notes

• New Features
  • Added comprehensive internationalization support enabling the app to display in multiple languages (Chinese, English, French, Japanese, Russian, Vietnamese).
  • Added language preference settings that users can configure and synchronize across all their devices.
  • API responses and error messages now display in the user's preferred language.

[coderabbitai]

Caution

Review failed

The pull request is closed.

Walkthrough

Implements comprehensive internationalization (i18n) support with go-i18n backend integration, context-aware language detection, API response helpers for localized messages, controller refactoring to use i18n, and frontend language preference settings with synchronization to user profile.

Changes

Cohort / File(s)	Summary
Backend i18n Infrastructure i18n/i18n.go, i18n/keys.go, i18n/locales/...yaml	Introduces complete i18n system with bundle setup, localizer caching, language detection from user settings/headers, and 150+ translation constants across domains. Supports zh/en with lazy initialization and thread-safe access.
API Response Helpers common/gin.go, constant/context_key.go	Adds ApiErrorI18n and ApiSuccessI18n functions for localized responses; introduces global TranslateMessage hook and ContextKeyLanguage constant for language storage in request context.
Controller Refactoring controller/token.go, controller/redemption.go, controller/user.go	Replaces hardcoded error messages with i18n-based ApiErrorI18n calls; centralizes validation (validateExpiredTime signature changed to accept context and return translated message); updates 50+ error paths to localized responses.
Middleware & Model Support middleware/i18n.go, model/user_cache.go, model/redemption.go, main.go	Adds i18n middleware for language detection priority (user setting → Accept-Language header → default); helper GetUserLanguage for caching; initializes i18n system and registers language loader during startup.
Frontend Language Settings web/src/components/settings/personal/cards/PreferencesSettings.jsx, web/src/context/User/index.jsx, web/src/hooks/common/useHeaderBar.js	New PreferencesSettings component with language selector; syncs user language preference to backend via PUT /api/user/self; extends UserProvider to sync saved language with i18n on load; updates handleLanguageChange to persist preference.
Frontend Localization Integration web/src/hooks/.../useTokensData.jsx, web/src/hooks/.../useRedemptionsData.jsx, web/src/hooks/.../useUsersData.jsx, web/src/hooks/.../useChannelsData.jsx	Replaces hardcoded success messages with translated strings using i18n t() function across token, redemption, user, and channel management hooks.
Locale Files web/src/i18n/locales/en.json, web/src/i18n/locales/zh.json, web/src/i18n/locales/fr.json, web/src/i18n/locales/ja.json, web/src/i18n/locales/ru.json, web/src/i18n/locales/vi.json	Adds 28+ translations across multiple languages for language preferences, performance monitoring controls, and system feature labels; existing keys remain unchanged.
Data Model & Dependencies dto/user_settings.go, go.mod	Extends UserSetting struct with Language field (json: language,omitempty); adds go-i18n v2.6.1 and samber/hot v0.11.0 dependencies; bumps indirect modules for text/sync/yaml support.

Sequence Diagram

sequenceDiagram
    participant Client as Client<br/>(Browser)
    participant Server as Server<br/>(Gin)
    participant i18n as i18n<br/>Module
    participant DB as Database
    participant Loader as UserLangLoader<br/>(Cache)

    Client->>Server: Request (Accept-Language header)
    Server->>i18n: I18n Middleware: DetectLanguage()
    
    alt User Setting Available
        i18n->>DB: Retrieve from UserContext.Setting
        DB-->>i18n: Language (zh/en)
    else Check User Cache
        i18n->>Loader: GetUserLanguage(userId)
        Loader->>DB: Query user cache
        DB-->>Loader: Cached language
        Loader-->>i18n: Language string
    else Parse Accept-Language
        i18n->>i18n: ParseAcceptLanguage(header)
        i18n-->>i18n: Normalized lang (zh/en)
    else Default
        i18n-->>i18n: DefaultLang (en)
    end
    
    i18n->>Server: Store lang in context (ContextKeyLanguage)
    Server-->>Client: Process request with language
    
    Server->>i18n: T(context, "token.name_too_long", args)
    i18n->>i18n: GetLocalizer(detectedLang)
    i18n-->>Server: Translated message
    Server-->>Client: JSON response with localized message

    Client->>Server: PUT /api/user/self {language: "zh"}
    Server->>DB: Update user.setting.language
    DB-->>Server: Confirmed
    Server-->>Client: Success response

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Estimated Code Review Effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly Related PRs

• PR #1341 — Refactors user settings into typed dto.UserSetting and adds context helpers; this PR extends that DTO with Language field and integrates i18n context handling, building directly on those foundational changes.
• PR #2808 — Extends i18n system with subscription-related translations and integrates i18n usage across controllers; overlaps on i18n infrastructure expansion and locale key additions.
• PR #1976 — Adds i18n translation keys and locale files for topup/billing features; both PRs expand translation coverage and controller i18n integration in the same domains.

Suggested Labels

enhancement, i18n, localization

Suggested Reviewers

• creamlike1024

Poem

🐰 A rabbit hops through languages bright,
From East to West, with translations in sight,
Each message now speaks in many a tongue,
The i18n song of the global is sung! 🌍✨

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch feat/backend-i18n

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