Outdated documentation in set_language() references removed session-based language storage

[Samriddha Kumar Tripathi]

The documentation and docstring for django.views.i18n.set_language() contain outdated information about session-based language storage, which was deprecated in Django 3.0 and removed in Django 4.0.

Affected locations:

1. Docstring in django/views/i18n.py: Current text says: "Redirect to a given URL while setting the chosen language in the session (if enabled) and in a cookie."

2. Documentation (i18n section): Current text says: "The view expects to be called via the POST method, with a language parameter set in request. If session support is enabled, the view saves the language choice in the user's session. It also saves the language choice in a cookie that is named django_language by default."

The issue:

The actual code in set_language() does NOT save the language to the session. According to the Django 3.0 release notes:

"To limit creation of sessions and hence favor some caching strategies, django.views.i18n.set_language() will stop setting the user's language in the session in Django 4.0. Since Django 2.1, the language is always stored in the LANGUAGE_COOKIE_NAME cookie."

Expected behavior:

Both the docstring and documentation should be updated to remove references to session storage and clarify that the language choice is stored only in the cookie (LANGUAGE_COOKIE_NAME, which defaults to django_language).

Credit: Issue reported by kid_alan_ on Discord.