# Vue: Managing locales
URL: https://generaltranslation.com/en-US/docs/vue/guides/managing-locales.mdx
Docs index: https://generaltranslation.com/llms.txt
Description: How to declare Vue locales, build a language switcher, and control reactive or reload-based changes.

Locale codes such as `en-US` and `fr` connect a user's language choice to the correct catalog and formatting rules. Configure the source and target locales, then use the locale composables inside your Vue components.

## Declare available locales [#declare]

Set the source locale and target locales in `gt.config.json`:

```json title="gt.config.json"
{
  "defaultLocale": "en",
  "locales": ["es", "fr", "de"]
}
```

`defaultLocale` is the language of your source content. `locales` lists the languages the CLI should generate.

Pass `defaultLocale` to [`createGT()`](/docs/vue/reference/functions/create-gt). Keep the target list for your language switcher:

```ts
const gt = createGT({
  defaultLocale: gtConfig.defaultLocale,
  loadTranslations,
});

const availableLocales = [gtConfig.defaultLocale, ...gtConfig.locales];
```

A plugin created with [`createGT()`](/docs/vue/reference/functions/create-gt) does not restrict locale codes to this list. Only offer supported values in your interface, and make the loader return an empty catalog or reject unsupported requests intentionally.

## Read the active locale [#read]

[`useLocale()`](/docs/vue/reference/composables/use-locale) returns a readonly Vue ref. Templates unwrap it automatically:

```vue
<script setup lang="ts">
import { watch } from 'vue';
import { useLocale } from 'gt-vue';

const locale = useLocale();

watch(locale, (nextLocale) => {
  document.documentElement.lang = nextLocale;
});
</script>

<template>
  <p>Active locale: {{ locale }}</p>
</template>
```

Read `locale.value` in ordinary script expressions. Components, computed values, and render effects that read the ref update after a reactive locale switch finishes.

## Build a language switcher [#switcher]

[`useSetLocale()`](/docs/vue/reference/composables/use-set-locale) returns an async setter. Await it so the interface can represent a pending load or handle a rejection:

```vue title="src/components/LocaleSwitcher.vue"
<script setup lang="ts">
import { ref } from 'vue';
import { useLocale, useSetLocale } from 'gt-vue';

const props = defineProps<{ locales: readonly string[] }>();
const locale = useLocale();
const setLocale = useSetLocale();
const changing = ref(false);

async function changeLocale(event: Event) {
  const target = event.target as HTMLSelectElement;
  changing.value = true;

  try {
    await setLocale(target.value);
  } finally {
    changing.value = false;
  }
}
</script>

<template>
  <select :value="locale" :disabled="changing" @change="changeLocale">
    <option v-for="code in props.locales" :key="code" :value="code">
      {{ code }}
    </option>
  </select>
</template>
```

With a [`createGT()`](/docs/vue/reference/functions/create-gt) plugin, the setter loads an uncached catalog before changing the locale. Successful results are cached. If requests overlap, only the latest request changes the active locale.

An empty catalog is a successful load: the locale changes and source content renders as the fallback. A rejected loader leaves the active locale and its cookie unchanged.

## Persist the locale [#persistence]

In a browser, the active locale is stored in a path-wide session cookie named `generaltranslation.locale`. When `locale` is omitted from [`createGT()`](/docs/vue/reference/functions/create-gt), that cookie wins over `defaultLocale`.

Set `localeCookieName` when the app must share another cookie with a router or server:

```ts
createGT({
  defaultLocale: 'en',
  localeCookieName: 'my-app.locale',
  loadTranslations,
});
```

Use [`useSetLocale()`](/docs/vue/reference/composables/use-set-locale) rather than writing the cookie directly. Browsers do not emit a reactive event for cookie changes, so an external write does not schedule a Vue render by itself.

## Choose reactive or reload-based switching [#runtime-mode]

The initialization mode determines what happens after the cookie changes:

- [`createGT()`](/docs/vue/reference/functions/create-gt) loads the catalog and updates reactive consumers without reloading the page.
- [`initializeGTSPA()`](/docs/vue/reference/functions/initialize-gt-spa) writes the cookie and reloads the document so module-level [`t()`](/docs/vue/reference/functions/t) calls execute again after preloading the new locale.

The SPA initializer accepts `locales` and falls back to `defaultLocale` when a saved or requested locale is unsupported. Follow [Developing with SPA translations](/docs/vue/guides/developing-spa-translations) when module-level translation requires that behavior.

For server rendering, resolve the request locale on the server and pass it explicitly to [`createGT()`](/docs/vue/reference/functions/create-gt). The explicit value overrides a stale browser cookie and keeps the server render and hydration locale aligned.

## Next steps

- /docs/vue/guides/configuring
- /docs/vue/guides/storing-translations
- /docs/vue/guides/developing-spa-translations
- /docs/vue/guides/translating-content

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