The Django 1.11 documentation says it should be there and I checked the github repo and it is not there.
In 1.10.7 it was still there.
It is actually in django.utils.translation instead of django.utils.translation.trans_real. (eg. pypugjs needs to be updated)
django.utils.translation
django.utils.translation.trans_real
Use the latest pypugjs release (5.0.1) to have it fixed!