maternal-app/docs/LOCALIZATION_IMPLEMENTATION_PLAN.md

Localization Implementation Plan

Created: October 3, 2025 Priority: HIGH (Pre-Launch) Estimated Duration: 2-3 days

Overview

Implement comprehensive internationalization (i18n) support for the Maternal App with 5 languages and measurement unit preferences.

Supported Languages

1. English (en-US) - Primary/Default
2. Spanish (es-ES)
3. French (fr-FR)
4. Portuguese (pt-BR)
5. Simplified Chinese (zh-CN)

Current Status

✅ Already Completed

• Backend multilanguage support for AI responses
• AI safety responses in 5 languages
• MultiLanguageService with language detection

❌ To Be Implemented

• Frontend i18next framework
• Translation files for all UI strings
• Language selector in onboarding
• Language selector in settings
• Date/time localization
• Measurement unit preferences (Metric/Imperial)
• Number formatting per locale

---

Phase 1: Framework Setup

1.1 Install Dependencies - latest versions only!

Files: package.json

npm install i18next react-i18next i18next-browser-languagedetector
npm install date-fns # Already installed, confirm locales

Packages:

• i18next - Core i18n framework
• react-i18next - React bindings
• i18next-browser-languagedetector - Auto-detect user language

1.2 Create i18n Configuration

File: lib/i18n/config.ts (NEW)

• Initialize i18next
• Configure language detector
• Set up fallback language (en-US)
• Configure interpolation
• Load translation resources

1.3 Create i18n Provider

File: components/providers/I18nProvider.tsx (NEW)

• Wrap app with I18nextProvider
• Initialize i18n on mount
• Handle language loading states

1.4 Update Root Layout

File: app/layout.tsx (MODIFY)

• Add I18nProvider to provider stack
• Set html lang attribute dynamically

---

Phase 2: Translation Files Structure

2.1 Directory Structure

locales/
├── en/
│   ├── common.json          # Common UI strings (buttons, labels, etc.)
│   ├── auth.json            # Authentication pages
│   ├── dashboard.json       # Dashboard/home page
│   ├── tracking.json        # Activity tracking
│   ├── children.json        # Child management
│   ├── family.json          # Family management
│   ├── ai.json              # AI assistant
│   ├── analytics.json       # Analytics/insights
│   ├── settings.json        # Settings page
│   ├── onboarding.json      # Onboarding flow
│   ├── errors.json          # Error messages
│   └── validation.json      # Form validation messages
├── es/
│   └── [same structure]
├── fr/
│   └── [same structure]
├── pt/
│   └── [same structure]
└── zh/
    └── [same structure]

2.2 Translation Keys Structure

Example - common.json:

{
  "nav": {
    "dashboard": "Dashboard",
    "track": "Track",
    "children": "Children",
    "family": "Family",
    "ai": "AI Assistant",
    "analytics": "Analytics",
    "settings": "Settings"
  },
  "buttons": {
    "save": "Save",
    "cancel": "Cancel",
    "delete": "Delete",
    "edit": "Edit",
    "add": "Add",
    "submit": "Submit",
    "back": "Back",
    "next": "Next",
    "confirm": "Confirm"
  },
  "units": {
    "metric": "Metric",
    "imperial": "Imperial",
    "ml": "ml",
    "oz": "oz",
    "cm": "cm",
    "in": "in",
    "kg": "kg",
    "lb": "lb"
  }
}

---

Phase 3: Custom Hooks

3.1 useTranslation Hook

File: hooks/useTranslation.ts (NEW)

• Re-export from react-i18next with type safety
• Custom hook for easier usage

3.2 useLocale Hook

File: hooks/useLocale.ts (NEW)

• Get current locale
• Change locale
• Get available locales
• Get locale display name

3.3 useFormatting Hook

File: hooks/useFormatting.ts (NEW)

• Format dates based on locale
• Format numbers based on locale
• Format currency based on locale
• Format units based on preference

---

Phase 4: Measurement Unit Preference

4.1 Backend Schema Update

File: src/database/migrations/V0XX_add_measurement_preference.sql (NEW)

ALTER TABLE users ADD COLUMN measurement_unit VARCHAR(10) DEFAULT 'metric';
-- Values: 'metric' or 'imperial'

4.2 Update User Entity

File: src/database/entities/user.entity.ts (MODIFY)

Add field:

@Column({ name: 'measurement_unit', default: 'metric' })
measurementUnit: 'metric' | 'imperial';

4.3 Update User DTOs

Files:

• src/modules/auth/dto/register.dto.ts (MODIFY)
• src/modules/auth/dto/update-profile.dto.ts (MODIFY)

Add optional measurementUnit field.

4.4 API Endpoints

File: src/modules/auth/auth.controller.ts (MODIFY)

• PATCH /api/v1/auth/profile - Include measurementUnit in update

---

Phase 5: Frontend User Preferences

5.1 Redux State

File: store/slices/userSlice.ts (MODIFY)

Add to user state:

interface UserState {
  // ... existing fields
  language: string;
  measurementUnit: 'metric' | 'imperial';
}

5.2 Language Selector Component

File: components/settings/LanguageSelector.tsx (NEW)

Features:

• Dropdown with 5 language options
• Flag icons for each language
• Updates user preference on change
• Persists to backend
• Updates i18n instance

5.3 Measurement Unit Selector Component

File: components/settings/MeasurementUnitSelector.tsx (NEW)

Features:

• Toggle or dropdown (Metric/Imperial)
• Updates user preference on change
• Persists to backend
• Shows example conversions

---

Phase 6: Onboarding Flow Integration

6.1 Update Onboarding Page

File: app/(auth)/onboarding/page.tsx (MODIFY)

Add new steps:

1. Language selection (Step 2)
2. Measurement unit selection (Step 3)

6.2 Onboarding Language Step Component

File: components/onboarding/LanguageStep.tsx (NEW)

• Large, visual language selector
• Show language names in native script
• Save to Redux state
• Update i18n immediately

6.3 Onboarding Measurement Step Component

File: components/onboarding/MeasurementStep.tsx (NEW)

• Visual metric/imperial selector
• Show examples (ml vs oz, cm vs in)
• Save to Redux state

6.4 Update Onboarding API Call

File: app/(auth)/onboarding/page.tsx (MODIFY)

Include language and measurementUnit in profile update call.

---

Phase 7: Settings Page Integration

7.1 Update Settings Page

File: app/settings/page.tsx (MODIFY)

Add new sections:

• Language & Region section
  • Language selector
  • Measurement unit selector

7.2 Settings UI Components

Files:

• components/settings/LanguageSettings.tsx (NEW)
• components/settings/MeasurementSettings.tsx (NEW)

---

Phase 8: Unit Conversion Utilities

8.1 Conversion Utility

File: lib/units/conversions.ts (NEW)

Functions:

• mlToOz(ml: number): number
• ozToMl(oz: number): number
• kgToLb(kg: number): number
• lbToKg(lb: number): number
• cmToIn(cm: number): number
• inToCm(in: number): number

8.2 Format Unit Hook

File: hooks/useUnitFormat.ts (NEW)

• Get user's measurement preference
• Format value with correct unit
• Convert between units
• Display with locale-specific formatting

---

Phase 9: Apply Localization Throughout App

9.1 Update All Pages

Replace hardcoded strings with translation keys:

Priority Pages:

1. Dashboard (app/page.tsx)

   • Nav items, headings, button labels
   • Activity type labels
   • Summary labels

2. Authentication (app/(auth)/)

   • Login, Register, Forgot Password
   • Form labels, placeholders, errors

3. Tracking (app/track/)

   • Feeding, Sleep, Diaper pages
   • Form labels, unit labels
   • Apply unit conversions

4. Children (app/children/page.tsx)

   • Child management labels
   • Form fields

5. Family (app/family/page.tsx)

   • Family management labels

6. AI Assistant (app/ai-assistant/page.tsx)

   • Chat interface labels
   • Placeholder text

7. Analytics (app/analytics/page.tsx)

   • Chart labels, insights

8. Settings (app/settings/page.tsx)

   • All settings labels

9.2 Update Components

Replace hardcoded strings in shared components:

• components/layouts/AppShell/ (navigation)
• components/common/ (buttons, dialogs)
• components/features/ (activity cards, etc.)

---

Phase 10: Date/Time Localization

10.1 Date Formatting Utility

File: lib/i18n/date-formats.ts (NEW)

Using date-fns with locales:

import { format } from 'date-fns';
import { enUS, es, fr, ptBR, zhCN } from 'date-fns/locale';

const locales = { en: enUS, es, fr, pt: ptBR, zh: zhCN };

export function formatDate(date: Date, formatStr: string, locale: string) {
  return format(date, formatStr, { locale: locales[locale] });
}

10.2 Update Date Displays

Apply locale-aware date formatting:

• Activity timestamps
• Child birth dates
• Analytics date ranges

---

Phase 11: Number Localization

11.1 Number Formatting Utility

File: lib/i18n/number-formats.ts (NEW)

Using Intl.NumberFormat:

export function formatNumber(value: number, locale: string) {
  return new Intl.NumberFormat(locale).format(value);
}

export function formatDecimal(value: number, locale: string, decimals = 1) {
  return new Intl.NumberFormat(locale, {
    minimumFractionDigits: decimals,
    maximumFractionDigits: decimals,
  }).format(value);
}

11.2 Apply Number Formatting

• Activity amounts (ml/oz)
• Sleep duration (hours)
• Weight/height measurements

---

Phase 12: Tracking Forms with Unit Preferences

12.1 Update Feeding Form

File: app/track/feeding/page.tsx (MODIFY)

• Show ml or oz input based on preference
• Convert to metric for API storage
• Display in user's preferred unit

12.2 Update Child Profile Form

File: app/children/page.tsx (MODIFY)

• Weight input (kg/lb)
• Height input (cm/in)
• Convert for API storage

12.3 Universal Input Component

File: components/forms/UnitInput.tsx (NEW)

Props:

• type: 'volume' | 'weight' | 'height'
• value: number
• onChange: (value: number) => void
• Auto-convert based on user preference

---

Phase 13: Translation Files Content

13.1 English Translations (Base)

Estimate: ~500-800 translation keys across all files

Create complete English translations for:

• All UI strings
• All form labels/placeholders
• All error messages
• All validation messages

13.2 Professional Translation

Recommendation: Use professional translation service for:

• Spanish (es-ES)
• French (fr-FR)
• Portuguese (pt-BR)
• Simplified Chinese (zh-CN)

Alternative: Use AI-assisted translation + native speaker review

---

Phase 14: Testing

14.1 Translation Coverage Test

• Verify all strings are externalized
• No hardcoded English strings remain
• All translation keys exist in all languages

14.2 Language Switching Test

• Switch between all 5 languages
• Verify UI updates correctly
• Verify no layout breaks

14.3 Unit Conversion Test

• Test all conversions (ml↔oz, kg↔lb, cm↔in)
• Verify correct rounding
• Verify storage in consistent units (metric)

14.4 Date/Time Test

• Verify dates display correctly per locale
• Test all date formats (short, long, relative)

14.5 RTL Support (Future)

Note: Chinese doesn't require RTL, but document for future Arabic support

---

Phase 15: Documentation

15.1 Update Implementation Gaps

File: docs/implementation-gaps.md (MODIFY)

Mark localization as ✅ COMPLETED

15.2 Developer Guide

File: docs/LOCALIZATION_GUIDE.md (NEW)

Document:

• How to add new translation keys
• How to add new languages
• Translation file structure
• Best practices

15.3 Update User Documentation

Document language and measurement preferences in user guide

---

Implementation Order

Day 1: Framework & Structure

1. ✅ Install dependencies
2. ✅ Create i18n configuration
3. ✅ Create i18n provider
4. ✅ Create hooks (useTranslation, useLocale, useFormatting)
5. ✅ Set up translation file structure
6. ✅ Create English base translations (common, auth, dashboard)

Day 2: Preferences & Components

7. ✅ Backend schema update for measurementUnit
8. ✅ Update User entity and DTOs
9. ✅ Create LanguageSelector component
10. ✅ Create MeasurementUnitSelector component
11. ✅ Update onboarding flow
12. ✅ Update settings page
13. ✅ Create unit conversion utilities

Day 3: Apply Throughout App

14. ✅ Update all pages with translations
15. ✅ Apply unit conversions to tracking forms
16. ✅ Apply date/time localization
17. ✅ Complete all English translations
18. ✅ Test language switching
19. ✅ Test unit conversions

Post-Implementation (Optional)

20. Professional translation for other 4 languages
21. Native speaker review
22. Documentation updates

---

Key Files Checklist

New Files (27 total)

• lib/i18n/config.ts
• components/providers/I18nProvider.tsx
• hooks/useLocale.ts
• hooks/useFormatting.ts
• hooks/useUnitFormat.ts
• lib/units/conversions.ts
• lib/i18n/date-formats.ts
• lib/i18n/number-formats.ts
• components/settings/LanguageSelector.tsx
• components/settings/MeasurementUnitSelector.tsx
• components/settings/LanguageSettings.tsx
• components/settings/MeasurementSettings.tsx
• components/onboarding/LanguageStep.tsx
• components/onboarding/MeasurementStep.tsx
• components/forms/UnitInput.tsx
• locales/en/*.json (11 files)
• locales/es/*.json (11 files - future)
• locales/fr/*.json (11 files - future)
• locales/pt/*.json (11 files - future)
• locales/zh/*.json (11 files - future)
• src/database/migrations/V0XX_add_measurement_preference.sql
• docs/LOCALIZATION_GUIDE.md

Modified Files (15 total)

• package.json
• app/layout.tsx
• store/slices/userSlice.ts
• src/database/entities/user.entity.ts
• src/modules/auth/dto/register.dto.ts
• src/modules/auth/dto/update-profile.dto.ts
• app/(auth)/onboarding/page.tsx
• app/settings/page.tsx
• app/page.tsx (dashboard)
• app/track/feeding/page.tsx
• app/track/sleep/page.tsx
• app/track/diaper/page.tsx
• app/children/page.tsx
• app/family/page.tsx
• docs/implementation-gaps.md

---

Success Criteria

✅ Functionality

• All 5 languages selectable and functional
• Language preference persists across sessions
• Measurement unit preference persists across sessions
• All UI strings externalized (no hardcoded English)
• Unit conversions work correctly (ml↔oz, kg↔lb, cm↔in)
• Dates display correctly per locale
• Numbers format correctly per locale

✅ User Experience

• Language can be selected in onboarding
• Language can be changed in settings
• Measurement unit can be selected in onboarding
• Measurement unit can be changed in settings
• UI updates immediately when language changes
• No layout breaks when changing languages
• Form inputs show correct units based on preference

✅ Technical

• All translation keys defined
• No missing translation warnings
• Type-safe translation usage (TypeScript)
• Backend stores preferences correctly
• Redux state syncs with backend

---

Notes

Translation Best Practices

1. Use namespaces to organize translations
2. Use interpolation for dynamic values: t('welcome', { name })
3. Use pluralization: t('items', { count })
4. Keep keys descriptive: auth.login.emailLabel not auth.e1
5. Avoid concatenation, use complete sentences

Unit Conversion Strategy

• Storage: Always store in metric (ml, kg, cm) in database
• Display: Convert to user's preferred unit for display
• Input: Accept user's preferred unit, convert to metric before API call
• Consistency: Ensure all measurements use the same preference

Performance Considerations

• Lazy load translation files per namespace
• Cache translations in browser
• Preload critical translations (common, errors)

Future Enhancements

• Add more languages (Arabic, German, Hindi, etc.)
• Add more units (temperature: °C/°F)
• Add regional date formats (MM/DD vs DD/MM)
• Add time format preferences (12h vs 24h)

---

Total Estimated Effort: 2-3 days Complexity: Medium Priority: HIGH (Pre-Launch) Dependencies: None (can start immediately)