code: def _get_fieldsets_post_form_or_formset(self, request, form, obj=None):
          
          base_fields = self.replace_orig_field(form.base_fields.keys())
          fields = base_fields + list(self.get_readonly_fields(request, obj))
          return [(None, {'fields': self.replace_orig_field(fields)})]
docs: Generic get_fieldsets code, shared by
          TranslationAdmin and TranslationInlineModelAdmin.