When an entity is translatable (ex. a node) and it has entity entity reference fields that are translatable (ex. a file field) the default_content_deploy exporter does not export any of the translated references.
1. Enable a second language (ex. French)
2. Create a translatable content type
3. Add a translatable file field
4. Create a node in the default language (en)
5. Upload an en PDF
6. Translate the node to fr
7. Upload a fr PDF
8. Export your node using default_content_deploy with references
You will find there is only one PDF file exported and that is the en PDF.
Iterate over translation language when building referenced entities.
Needs review
2.0
Code
This patch is definitely needed. If users add a media item to French content, that is unique to that language (not a translation of the English media item), then that media item would not be exported as a reference.
Updating patch slightly to remove $language which is not used in this method.