Source

File: wp-includes/class-wp-locale-switcher.php

private function change_locale( $locale ) {
		// Reset translation availability information.
		_get_path_to_translation( null, true );

		$this->load_translations( $locale );

		$GLOBALS['wp_locale'] = new WP_Locale();

		/**
		 * Fires when the locale is switched to or restored.
		 *
		 * @since 4.7.0
		 *
		 * @param string $locale The new locale.
		 */
		do_action( 'change_locale', $locale );
	}