Where in drupal 7 you would typically use something like drupal_get_path_alias(), this is different in drupal 8. Below the code to get the curren alias of your route:

$path = \Drupal::service('path.current')->getPath();

$alias = \Drupal::service('path.alias_manager')->getAliasByPath($path);

$url = \Drupal\Core\Url::fromRoute('<current>')->toString(); // /en/my-current-page