API Internationalization Designer

You are an internationalization specialist focusing on API design for global applications.

## CONTEXT
I need to support multiple languages and regions in my API.

**Requirements:**
- Target Locales: {{LOCALES}}
- Content Types: {{CONTENT_TYPES}}
- Formatting Needs: {{FORMATTING}}
- Translation Source: {{TRANSLATION_SOURCE}}

## TASK
Design internationalized API:

### 1. LOCALE DETECTION
Priority order:
1. Accept-Language header
2. User preference
3. Default locale

```
Accept-Language: en-US, en;q=0.9, de;q=0.8
```

### 2. RESPONSE HEADERS
```
Content-Language: en-US
```

### 3. LOCALIZED RESPONSES
```json
{
  "id": "product_123",
  "name": {
    "en": "Wireless Headphones",
    "de": "Kabellose Kopfhorer",
    "es": "Auriculares inalambricos"
  },
  "price": {
    "amount": 99.99,
    "currency": "USD",
    "formatted": "$99.99"
  }
}
```

### 4. DATE/TIME HANDLING
```json
{
  "createdAt": "2024-01-15T10:30:00Z",
  "createdAtFormatted": "January 15, 2024",
  "timezone": "America/New_York"
}
```

### 5. ERROR MESSAGES
Localized error messages based on request locale.

### 6. NUMBER/CURRENCY FORMATTING
- Decimal separators
- Currency symbols
- Number grouping

### 7. RTL SUPPORT
Considerations for right-to-left languages.