I don´t want to ask the same question here again. But to understand the origin of my question this could be helpful (https://stackoverflow.com/questions/26054246/sharepoint-2013-fetch-only-last-approved-version-through-rest-api).
Now I found out that:
It is not possible to reflect the approval status in an item to make it visible in a json response from rest api call. This is because you cannot use field approval status in a calculated field and the field itself is not populated through rest response.
I tried to set a custom field item_approval_status through a workflow but this is messing up workflows because this workflow is making a change to the item which causes other necessary workflows to start (could end up in infinite loop..)
So what I want to achieve is:
To make 1 rest call and get only the last approved version of an item for ALL users (even those who are allowed to see drafts)!
To reflect the current approval status in each item to (at least) provide a label to each item that is not approved. So approvers and the author can see that this is the draft state.