Problem/Motivation
If the source comment type ID (bundle) is longer 32 characters, then the related language content settings migration d7_language_content_comment_settings triggers MigrateException (and fails migration)
The logged migration message is:
Missing bundle entity, entity type comment_type, entity id comment_node_a_random_node_type_id. ([docroot]/core/lib/Drupal/Core/Entity/EntityType.php:877)
Steps to reproduce
Create a content type with a long bundle name (at least 21 chars), enable translation for this particular type, and migrate.
Proposed resolution
The process pipeline of the target_bundle destination property has to use migration_lookup.