determine_locale()

determine_locale(): string

function determine_locale() {
	/**
	 * Filters the locale for the current request prior to the default determination process.
	 *
	 * Using this filter allows to override the default logic, effectively short-circuiting the function.
	 *
	 * @since 5.0.0
	 *
	 * @param string|null $locale The locale to return and short-circuit. Default null.
	 */
	$determined_locale = apply_filters( 'pre_determine_locale', null );

	if ( $determined_locale && is_string( $determined_locale ) ) {
		return $determined_locale;
	}

	if (
		isset( $GLOBALS['pagenow'] ) && 'wp-login.php' === $GLOBALS['pagenow'] &&
		( ! empty( $_GET['wp_lang'] ) || ! empty( $_COOKIE['wp_lang'] ) )
	) {
		if ( ! empty( $_GET['wp_lang'] ) ) {
			$determined_locale = sanitize_locale_name( $_GET['wp_lang'] );
		} else {
			$determined_locale = sanitize_locale_name( $_COOKIE['wp_lang'] );
		}
	} elseif (
		is_admin() ||
		( isset( $_GET['_locale'] ) && 'user' === $_GET['_locale'] && wp_is_json_request() )
	) {
		$determined_locale = get_user_locale();
	} elseif (
		( ! empty( $_REQUEST['language'] ) || isset( $GLOBALS['wp_local_package'] ) )
		&& wp_installing()
	) {
		if ( ! empty( $_REQUEST['language'] ) ) {
			$determined_locale = sanitize_locale_name( $_REQUEST['language'] );
		} else {
			$determined_locale = $GLOBALS['wp_local_package'];
		}
	}

	if ( ! $determined_locale ) {
		$determined_locale = get_locale();
	}

	/**
	 * Filters the locale for the current request.
	 *
	 * @since 5.0.0
	 *
	 * @param string $determined_locale The locale.
	 */
	return apply_filters( 'determine_locale', $determined_locale );
}