[upstream] Translated field collections are not migrated correctly

Thanks for your report!

The two most plausible answers:

1. Your Drupal 7 site does not have all of its modules up-to-date, in particular Field Collections and translation-related modules. Please make sure they're up-to-date before running the migration!
2. This is a bug in https://www.drupal.org/project/paragraphs_migration → — perhaps it does not correctly handle migrations from translated Field Collections.

I'm hoping it's the first thing (which is easy & fast to verify). If it's the second, we'll have to move this issue to the https://www.drupal.org/project/issues/paragraphs_migration → issue queue.

I suspect/fear it might be the second, because there's only one multilingual/translation issue that I can find: #3285020: Find out why multilingual multifield migrations are failing on PostgreSQL → , but it's when the D7 source uses Multifield, not Field Collection.

It seems to be a problem with paragraph migration itself. Everything on my side seems to be OK.
There is a proposed solution in https://www.drupal.org/project/paragraphs/issues/3160679 ✨ Field Collection Node content translation source plugin Needs review

As the documentation of Acquia Migrate points out that it will provide multilingual installations I thought that the migration of multilingual field_collections should work out of the box ;-)

Yes. We tested many things. But there's an infinite number of module + configuration combinations, it is physically impossible to test every permutation.