> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/4000-to-4002/aur4000.md).

# AUR4000

## Error Message

`AUR4000: Translation key not found`

## Description

This error occurs when the i18n system cannot find a translation for the requested key in any of the loaded translation resources. This typically happens when:

1. The translation key doesn't exist in the current locale's translation files
2. The translation files haven't been loaded properly
3. There's a typo in the translation key
4. The fallback locale doesn't contain the key either

## Common Scenarios

### Missing Translation Key

```typescript
// Translation file (en.json)
{
  "welcome": "Welcome",
  "goodbye": "Goodbye"
}

// Template usage
<template>
  <p>${'hello' & t}</p> <!-- AUR4000: 'hello' key doesn't exist -->
  <p>${'welcome' & t}</p> <!-- ✅ Works fine -->
</template>
```

### Typo in Translation Key

```typescript
// ❌ Wrong: Typo in key
<p>${'welcom' & t}</p> <!-- Missing 'e' at the end -->

// ✅ Correct: Proper key
<p>${'welcome' & t}</p>
```

## Solutions

### 1. **Add the Missing Translation Key**

```json
// en.json
{
  "welcome": "Welcome",
  "hello": "Hello",
  "goodbye": "Goodbye"
}
```

### 2. **Verify Translation Files Are Loaded**

```typescript
import { I18N } from '@aurelia/i18n';

export class MyApp {
  constructor(private i18n: I18N) {}
  
  async attached() {
    // Ensure translations are loaded
    await this.i18n.setLocale('en');
  }
}
```

### 3. **Use Fallback Values**

```html
<!-- Provide fallback text -->
<p>${'missing-key' & t : 'Default Text'}</p>
```

### 4. **Check Key Existence Programmatically**

```typescript
export class MyComponent {
  constructor(private i18n: I18N) {}
  
  getTranslation(key: string) {
    if (this.i18n.tr.hasKey(key)) {
      return this.i18n.tr(key);
    }
    return `Missing translation: ${key}`;
  }
}
```

## Debugging Tips

1. **Check Console**: Look for i18n loading errors in browser console
2. **Verify File Structure**: Ensure translation files are in the correct location
3. **Test Key Existence**: Use browser dev tools to check loaded translations
4. **Fallback Locale**: Ensure fallback locale contains all necessary keys


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