Source

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

public function switch_to_locale( $locale ) {
		$current_locale = determine_locale();
		if ( $current_locale === $locale ) {
			return false;
		}

		if ( ! in_array( $locale, $this->available_languages, true ) ) {
			return false;
		}

		$this->locales[] = $locale;

		$this->change_locale( $locale );

		/**
		 * Fires when the locale is switched.
		 *
		 * @since 4.7.0
		 *
		 * @param string $locale The new locale.
		 */
		do_action( 'switch_locale', $locale );

		return true;
	}