Multilingual comments in Drupal 8
At this moment in my team, we have identified 3 bugs around this, and to make this works you need to apply this 3 patches:

https://www.drupal.org/project/drupal/issues/2751269#comment-12559117

https://www.drupal.org/comment/12521645#comment-12521645

https://www.drupal.org/comment/12561153#comment-12561153