I'm trying to migrate images from a file field on a multy-language site - migrated from Drupal 6. Most of the pages on the website are from Bulgarian source language and they are translated to English, but there are a few, which was built with English source and translated to Bulgarian. Usually the teaser images for both websites are one and the same file uploaded 2 times, so they are duplicates.
Using the yml-migrate_file_to_media_migration_media generator if I set the source language to Bulgarian and add English for a translation language the images to all of the fields with core Bulgarian language are imported, but not their translated to English pages. Also the fields with core English language do not have imported media entities for Bulgarian, but there are ones in their core English version.
If I set in the yml configuration process the core language to English and translations to Bulgarian it behaves the same way - only the English core pages and the Bulgarian pages with core Bulgarian are properly updated. The translated to Bulgarian language pages and the ones translated to English are untouched.
If I skip adding translation language into yml generation process it acts just the same as if I use en source and bg for a translation..
All the tests I do with fresh imported sql file with no transfer_file_to_media_entity tables following this guide - https://texascreative.com/blog/basic-migration-file-fields-media-entities-fields-drupal-8