Investigation needed: ModelAdmin's get_object

In #150, we talked about an issue with `ModelAdmin.get_object`.
It uses `self.get_queryset` to fetch the object. However, as `get_queryset` uses an `untranslated()` queryset, that automatically tries to load fallback translations, it is very likely it may, under some circumstances, load a wrong translation and overwrite it when submitting changes to an instance.

Fix 77669eed0543188cca302fec363304561e58786b was suggested, but it bypassed any overriden `get_queryset`, which would break the normal way of restricting editable instances.

- Further investigation on the exact circumstances in which this can happen would be needed.
- Even better, fixing the code so that `get_object` cannot load a wrong translation in the first place.