# Localize Utilities
URL: /docs/native/expo/localize

Device locale, timezone, and formatting utilities with react-native-localize fallback.

## Overview

The `localize` module provides device locale detection, timezone, date/number/currency formatting, and measurement system detection. It requires `react-native-localize` for accurate native locale data and falls back to `Intl` APIs when unavailable.

## Installation

```bash
npx expo install react-native-localize
```

**Dependencies:**
- [react-native-localize](https://www.npmjs.com/package/react-native-localize)

### Expo Configuration

Add `react-native-localize` as a plugin in your `app.config.ts` with the locales your app supports:

```ts
{
  plugins: [
    [
      'react-native-localize',
      { locales: ['en', 'tr', 'de', 'fr'] }
    ]
  ]
}
```

> **Note:** Without this plugin config, locale detection may not work correctly on iOS. The `locales` array determines which languages your app declares support for.

## Usage

```tsx
import {
  getDeviceLocale,
  getDeviceLanguage,
  getDeviceCountry,
  getDeviceTimeZone,
  uses24HourClock,
  usesMetricSystem,
  formatDate,
  formatNumber,
  formatCurrency,
} from '@/lib/docyrus/localize';

// Device info
const locale = getDeviceLocale();        // 'tr-TR'
const lang = getDeviceLanguage();        // 'tr'
const country = getDeviceCountry();      // 'TR'
const tz = getDeviceTimeZone();          // 'Europe/Istanbul'
const is24h = uses24HourClock();         // true
const metric = usesMetricSystem();       // true

// Formatting
formatDate(new Date(), { dateStyle: 'long' });   // '5 Mart 2026'
formatNumber(1234.56);                            // '1.234,56'
formatCurrency(99.99, 'TRY');                     // '₺99,99'
```

## API Reference

### Device Info

| Function | Return Type | Description |
|----------|-------------|-------------|
| `getDeviceLocale()` | `string` | Full locale tag (e.g., `'tr-TR'`). Falls back to `'en-US'` |
| `getDeviceLanguage()` | `string` | Language code (e.g., `'tr'`). Falls back to `'en'` |
| `getDeviceCountry()` | `string \| undefined` | Country code (e.g., `'TR'`) |
| `getDeviceTimeZone()` | `string` | IANA timezone (e.g., `'Europe/Istanbul'`). Falls back to `'UTC'` |
| `uses24HourClock()` | `boolean` | Whether device uses 24-hour clock |
| `usesMetricSystem()` | `boolean` | Whether device uses metric system |
| `getPreferredLocales()` | `string[]` | All preferred locale tags |

### Formatting

| Function | Parameters | Description |
|----------|-----------|-------------|
| `formatNumber(value, options?, locale?)` | `number, Intl.NumberFormatOptions?, string?` | Locale-aware number formatting |
| `formatDate(date, options?, locale?)` | `Date, Intl.DateTimeFormatOptions?, string?` | Locale-aware date formatting |
| `formatCurrency(value, currencyCode?, locale?)` | `number, string?, string?` | Currency formatting (default: `'USD'`) |
| `getCurrencySymbol(currencyCode)` | `string` | Get currency symbol (e.g., `'₺'` for `'TRY'`) |

## Fallback Behavior

| Feature | With `react-native-localize` | Without (Intl fallback) |
|---------|------------------------------|------------------------|
| Locale detection | Device's preferred locale list | `Intl.DateTimeFormat` resolved locale |
| Timezone | `RNLocalize.getTimeZone()` | `Intl.DateTimeFormat` resolved timezone |
| 24h clock | `RNLocalize.uses24HourClock()` | AM/PM presence check |
| Metric system | `RNLocalize.usesMetricSystem()` | Country code heuristic (US, LR, MM → imperial) |

## Compatibility

| Platform | Support |
|----------|---------|
| Expo Go | Yes |
| Dev Client | Yes |
| Bare RN | Yes (auto-linked) |