# Switch the Front-End Language With ?lang=

> Lets visitors switch the theme and plugin interface language with a ?lang=fr_FR link; the choice is remembered in a cookie and limited to languages you allow.

- Type: PHP
- Runs: Run everywhere
- Category: [Multilingual](https://wpide.com/library/category/multilingual/)
- Tags: locale, language-switcher, cookie
- Author: WPIDE Team
- Installs: 0
- Updated: 2026-10-28
- Page: https://wpide.com/library/i18n-lang-query-switcher/

## Code

```php
$wpide_allowed = array( 'en_US', 'fr_FR', 'de_DE', 'es_ES' ); // Installed locales visitors may pick.

add_filter( 'determine_locale', function ( $locale ) use ( $wpide_allowed ) {
    if ( is_admin() ) {
        return $locale;
    }

    $pick = '';
    if ( isset( $_GET['lang'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification
        $pick = sanitize_text_field( wp_unslash( $_GET['lang'] ) ); // phpcs:ignore WordPress.Security.NonceVerification
    } elseif ( isset( $_COOKIE['wpide_lang'] ) ) {
        $pick = sanitize_text_field( wp_unslash( $_COOKIE['wpide_lang'] ) );
    }

    return in_array( $pick, $wpide_allowed, true ) ? $pick : $locale;
}, 20 );

add_action( 'init', function () use ( $wpide_allowed ) {
    if ( is_admin() || ! isset( $_GET['lang'] ) || headers_sent() ) { // phpcs:ignore WordPress.Security.NonceVerification
        return;
    }

    $pick = sanitize_text_field( wp_unslash( $_GET['lang'] ) ); // phpcs:ignore WordPress.Security.NonceVerification

    if ( in_array( $pick, $wpide_allowed, true ) ) {
        setcookie( 'wpide_lang', $pick, time() + YEAR_IN_SECONDS, COOKIEPATH, COOKIE_DOMAIN, is_ssl(), true );
    }
} );
```

## Notes

Only switches interface strings that have installed translations, not your post content. Install the languages in Settings > General first.

## How to use it

Install the free WPIDE plugin (https://wordpress.org/plugins/wpide/), find "Switch the Front-End Language With ?lang=" in its snippet library and add it in one click; or create a new PHP snippet in WPIDE (or any code snippets plugin) and paste the code above. More snippets: https://wpide.com/library/