> ## Documentation Index
> Fetch the complete documentation index at: https://docs.supernote.com/llms.txt
> Use this file to discover all available pages before exploring further.

# registerLangListener

> Listen for system language changes.

```ts theme={null}
registerLangListener(langListener: PluginEventListener): PluginEventSubscription;
```

Listens for system language changes. When the system language switches, it triggers the callback and provides the language code string.

**Parameters**

| Parameter      | Type                  | Description                                                                              |
| -------------- | --------------------- | ---------------------------------------------------------------------------------------- |
| `langListener` | `PluginEventListener` | Language change listener that implements `onMsg(msg)`. `msg` is the language code string |

**Returns**

* `PluginEventSubscription`: subscription object. Call `remove()` to unregister the listener

## Language Codes

| Language            | Code    |
| ------------------- | ------- |
| English             | `en`    |
| Simplified Chinese  | `zh_CN` |
| Traditional Chinese | `zh_TW` |
| Japanese            | `ja`    |

## Type Definitions

### PluginEventListener

```ts theme={null}
interface PluginEventListener {
 onMsg(msg: string): void;
}
```

**Description**

* `onMsg(msg)`: triggered when the system language changes
* `msg`: language code (see "Language Codes")

### PluginEventSubscription

```ts theme={null}
type PluginEventSubscription = {
 remove(): void;
};
```

## Example

```ts wrap theme={null}
import { PluginManager } from 'sn-plugin-lib';

/**
 * Example: listen for system language changes.
 */
export async function exampleRegisterLangListener() {
 const sub = PluginManager.registerLangListener({
 onMsg(langCode) {
 console.log('lang changed:', langCode);
 },
 });
 return sub;
}
```