def UserRegistration(request):
    if request.method == 'POST':
        username = request.POST['fn'].capitalize() + ' ' + request.POST['ln'
            ].capitalize()
newuser = User.objects.create_user(username=username, email=request.POST[
    'email'], password=request.POST['pw'])
newuser.first_name = request.POST['fn'].capitalize()
newuser.last_name = request.POST['ln'].capitalize()
newuser._language = request.POST['language']
newuser._field = request.POST['field']
newuser._otherfield = request.POST['otherfield']
newuser.save()
return HttpResponse(username)
post_save.connect(create_user_account, sender=User)
Передать дополнительные параметры в сигнал post_save