Pass additional parameters to post_save signal

Both User.objects.create_user and User.objects.create immediately triggers the post_save handler, because the save is called in the UserManager create_user. So I cannot imagine how Jorge's answer can work (at least if you want the save to be triggered only once - why would you trigger it twice???). What you want to do is to look into what create_user does, dissect it and this way you can really control when the save is called:

# Function to Create user Account/Profile
def create_user_account(sender, instance, created, **kwargs):
    if created:
        attrs_needed = ['_language', '_field', '_otherfield']
        if all(hasattr(instance, attr) for attr in attr_needed):
            models.Account.objects.create(
                user=instance, 
                language=instance._language, 
                field=instance._field,
                otherfield=instance._otherfield)

# Create User / User Registration
def UserRegistration(request):
  if request.method == 'POST':
    username = request.POST['fn'].capitalize() + ' ' + request.POST['ln'].capitalize()
    # CREATE USER
    newuser = User(
        username=username,
        email=request.POST['email'],
        first_name=request.POST['fn'].capitalize()
        last_name = request.POST['ln'].capitalize()
    )
    newuser.set_password(request.POST['pw'])

    # Set some extra attrs to the instance to be used in the handler.
    newuser._language = request.POST['language']
    newuser._field = request.POST['field']
    newuser._otherfield = request.POST['otherfield']
    newuser.save()  # Now this will be really the first save which is called

  return HttpResponse(username)

#Post Save handler to create user Account/Profile
post_save.connect(create_user_account, sender=User, weak=False)

Note that I also use the weak=False when I hook up the handler.

What I do is to set some '_attrs' to the instance and then use them in the signal handler.

I imagine your case could be:

# Function to Create user Account/Profile
def create_user_account(sender, instance, created, **kwargs):
    if created:
        attrs_needed = ['_language', '_field', '_otherfield']
        if all(hasattr(instance, attr) for attr in attr_needed):
            models.Account.objects.create(
                user=instance, 
                language=instance._language, 
                field=instance._field,
                otherfield=instance._otherfield)

# Create User / User Registration
def UserRegistration(request):
  if request.method == 'POST':
    username = request.POST['fn'].capitalize() + ' ' + request.POST['ln'].capitalize()
    # CREATE USER
    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()

    # Set some extra attrs to the instance to be used in the handler.
    newuser._language = request.POST['language']
    newuser._field = request.POST['field']
    newuser._otherfield = request.POST['otherfield']
    newuser.save()


  return HttpResponse(username)

#Post Save handler to create user Account/Profile
post_save.connect(create_user_account, sender=User)

I hate to do this, and I imagine it can breaks in horrible ways, and is hard to debug sometimes, also there is no a strict way to force the data needed for the handler, one could define a signal_data(data, signal, instance) to define the data needed for the signal handler for a particular instance.

A nice option that I haven't tried is to use methods of the instance as signal's handlers and maybe we can use a more structured way to pass the data.

Bye.