How deal with taxonomy term parameter in multilingue site?
You must edit your route to be like this, /myroute/{alias}.

Then you can load the term in your controller like this:

public function index($alias) {
  // Find the term by path alias.
  $path = \Drupal::service('path_alias.manager')-&gt;getPathByAlias($alias);
  if (preg_match('/taxonomy\/term\/(\d+)/', $path, $matches)) {
    $term = $this-&gt;entityTypeManager-&gt;getStorage('taxonomy_term')-&gt;load($matches[1]);
  }
  if (isset($term) &amp;&amp; $term instanceof TermInterface) {
    $term_id = $term-&gt;id();
  }
}


NB: The path_alias.manager service is added in Drupal 8.8.x, if you use an older version you must use the path.alias_manager service instead.