TmgmtConfigRouteSubscriber.php

<?php

namespace Drupal\tmgmt_config\Routing;

use Drupal\Core\Routing\RouteSubscriberBase;
use Drupal\Core\Routing\RoutingEvents;
use Symfony\Component\Routing\RouteCollection;

/**
 * Subscriber to alter entity translation routes.
 */
class TmgmtConfigRouteSubscriber extends RouteSubscriberBase {

  /**
   * {@inheritdoc}
   */
  protected function alterRoutes(RouteCollection $collection) {

    // Look for routes that use  ContentTranslationController and change it
    // to our subclass.
    foreach ($collection as $route) {
      if ($route
        ->getDefault('_controller') == '\\Drupal\\config_translation\\Controller\\ConfigTranslationController::itemPage') {
        $route
          ->setDefault('_controller', '\\Drupal\\tmgmt_config\\Controller\\ConfigTranslationControllerOverride::itemPage');
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() : array {
    $events = parent::getSubscribedEvents();

    // \Drupal\config_translation\Routing\RouteSubscriber is -110,
    // make sure we are later.
    $events[RoutingEvents::ALTER] = array(
      'onAlterRoutes',
      -111,
    );
    return $events;
  }

}