While working with https://www.drupal.org/project/content_moderation we encountered an error: InvalidArgumentException: Invalid translation language (es) specified. in Drupal\Core\Entity\ContentEntityBase->addTranslation() (line 958 of core/lib/Drupal/Core/Entity/ContentEntityBase.php).
The site has three languages EN, ES, PT
1. Create an EN node and keep it as Draft (Unpublished)
2. Create its ES translation and keep it as Draft (Unpublished)
3. Create its PT translation and keep it as Draft (Unpublished)
4. Publish its source language (EN)
5. Publish its PT translation
5. Delete ES translation
6. Edit the PT translation and create a new Draft (Unpublished) version
7. Added ES translation
At this point we can see the error.
We believe this is caused by https://www.drupal.org/project/drupal/issues/2860097.