public function test_switch_to_site_locale_if_user_locale_is_set() {
    global $l10n, $wp_locale_switcher;

    $site_locale = get_locale();

    $user_id = $this->factory()->user->create(
      array(
        'role'   => 'administrator',
        'locale' => 'de_DE',
      )
    );

    wp_set_current_user( $user_id );
    set_current_screen( 'dashboard' );

    $locale_switcher = clone $wp_locale_switcher;

    $wp_locale_switcher = new WP_Locale_Switcher();
    $wp_locale_switcher->init();

    $user_locale = get_user_locale();

    $this->assertSame( 'de_DE', $user_locale );

    load_default_textdomain( $user_locale );
    $language_header_before_switch = $l10n['default']->headers['Language']; // de_DE

    $locale_switched_user_locale  = switch_to_locale( $user_locale ); // False.
    $locale_switched_site_locale  = switch_to_locale( $site_locale ); // True.
    $site_locale_after_switch     = get_locale();
    $language_header_after_switch = isset( $l10n['default'] ); // en_US

    restore_current_locale();

    $language_header_after_restore = $l10n['default']->headers['Language']; // de_DE

    $wp_locale_switcher = $locale_switcher;

    set_current_screen( 'front' );

    $this->assertFalse( $locale_switched_user_locale );
    $this->assertTrue( $locale_switched_site_locale );
    $this->assertSame( $site_locale, $site_locale_after_switch );
    $this->assertSame( 'de_DE', $language_header_before_switch );
    $this->assertFalse( $language_header_after_switch );
    $this->assertSame( 'de_DE', $language_header_after_restore );
  }