---
tags: brew-js
---

# useI18n

Allows detection of browser language preferences and provide ways to define app's current language explicitly or through router.

import brew from "brew-js/core";
import I18n from "brew/extensions/i18n";

brew.with(I18n)(app => {
    app.useI18n(options);
});

## Options

### `languages`

A list of available languages.

### `detectLanguage`

<span style="background: lightblue;padding:.25em .75em;border-radius:1em;font-weight:bold">v0.4.8</span>

detectLanguage?: boolean;

Whether to detect language from browser preferences.

:::info
For best interoperabilitiy, it is recommended to use standard BCP language code in the `languages` list.
:::

### `defaultLanguage`

defaultLanguage?: string;

### `routeParam`

When defined, the current language will be reflected on the specified route parameters. Updating either `app.language` or `app.route[routeParam]` will cause the other to change.

If the route parameter resolves to a language not defined in the `languages` list, the defafult language will be set instead and will cause the app to redirect to the corresponding path.

:::warning
Note that the route parameter will subject to constraints given by the allowed routes. If constraint is needed on route parameter, be sure it matches the available languages.
:::

## Listening for language change

app.watch('language', (newLanguage) => {
    // ...
});