Setting User Language on Login in Django

There are multiple approaches to set a user's language preference on login in Django. While response.set_cookie() is one common method, it requires a response object which isn't available in the user_logged_in signal context.

Alternative Approaches

1. Using Middleware

You can create a custom middleware that checks if a user is authenticated and sets the language based on their preference:

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from django.utils import translation
from django.conf import settings

class UserLanguageMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        if request.user.is_authenticated and hasattr(request.user, 'language'):
            translation.activate(request.user.language)
            request.LANGUAGE_CODE = translation.get_language()
        
        response = self.get_response(request)
        
        # Set the language cookie if user is authenticated
        if request.user.is_authenticated and hasattr(request.user, 'language'):
            response.set_cookie(
                settings.LANGUAGE_COOKIE_NAME, 
                request.user.language,
                max_age=settings.LANGUAGE_COOKIE_AGE,
                path=settings.LANGUAGE_COOKIE_PATH,
                domain=settings.LANGUAGE_COOKIE_DOMAIN,
                secure=settings.LANGUAGE_COOKIE_SECURE,
                httponly=settings.LANGUAGE_COOKIE_HTTPONLY,
                samesite=settings.LANGUAGE_COOKIE_SAMESITE,
            )
        
        return response

Add this middleware to your MIDDLEWARE setting after the authentication middleware.

2. Using a Login View Decorator

If you're using function-based views for login, you can decorate them:

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from django.utils import translation
from functools import wraps

def set_user_language(view_func):
    @wraps(view_func)
    def wrapper(request, *args, **kwargs):
        response = view_func(request, *args, **kwargs)
        
        # After successful login, set language cookie
        if request.user.is_authenticated and hasattr(request.user, 'language'):
            response.set_cookie(
                settings.LANGUAGE_COOKIE_NAME,
                request.user.language
            )
        
        return response
    return wrapper

@set_user_language
def my_login_view(request):
    # Your login logic here
    pass

3. Overriding LoginView for Class-Based Views

If you're using Django's built-in LoginView, you can extend it:

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from django.contrib.auth.views import LoginView
from django.conf import settings

class CustomLoginView(LoginView):
    def form_valid(self, form):
        response = super().form_valid(form)
        
        # Set language cookie after successful login
        if self.request.user.is_authenticated and hasattr(self.request.user, 'language'):
            response.set_cookie(
                settings.LANGUAGE_COOKIE_NAME,
                self.request.user.language
            )
        
        return response

4. Using translation.override() in Signal Handler

For the admin interface or when you can't modify the response directly:

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from django.contrib.auth.signals import user_logged_in
from django.dispatch import receiver
from django.utils import translation

@receiver(user_logged_in)
def set_user_language(sender, user, request, **kwargs):
    if hasattr(user, 'language'):
        # This affects the current request only
        translation.activate(user.language)
        request.LANGUAGE_CODE = translation.get_language()
        
        # For subsequent requests, you'll need middleware or cookies

Recommendation

The middleware approach is the most comprehensive solution as it works for both admin and frontend login processes and ensures the language preference is applied consistently across the application.