Resolved
Resolved in: 1.9.0
Overview of the issue
If you are using a Group field, you cannot have different translation preferences for the subfields inside it. If your subfields require different translation preferences, add them as regular fields, not part of a Group field.
Workaround
Currently, you can only Copy the Group field, which copies all of the associated subfields as well. If you set any other translation preference for a Group field, the subfields will not be displayed in secondary languages.
The workaround does not work for the Groups on the Attachment page…
Could you create the forum ticket for this and share a link here?