Store the current language in a cookie rather than the session

[msiedlarek]

Related discussion

​http://groups.google.com/d/topic/django-developers/8THmJSioj4U/discussion

Problem summary

The problem is that even for non-logged users their language is stored in session (if it's supported or in the cookie otherwise). That creates a session for every client, which makes serving static (ofc I mean static, but not media) content through an upstream cache (such as Squid) really inefficient. I suppose selected language is not that secret to protect it by storing in session, and cookie is just ok. For cookie-varying cache it's a huge difference.

Solution proposal

There is a setting named LANGUAGE_COOKIE_NAME which never gets used if you use session based cookies. The file cookie is just never saved. But if there were an option to save data in the session and also save the LANGUAGE_COOKIE as a file separately - then it would also persist after logout and solve the issue with languages after the session gets destroyed.

(...)

I would propose to have the set_language() view with options to set it as a file based cookie or a session.

(...)

It would allow the language file based cookie to have a very long expire date and the session would still be usable for storing secure data.

[Luke Plant]

This is proposing the same thing as #12794, but for a different reason.

#13217 is related, but the solution proposed here was not proposed there, and doesn't have the same issues that caused the WONTFIX on that ticket. This change would help that problem if the cache is able to cache by language cookie.

I'm not in favour of yet another setting if we can avoid it - we need to know if there are any downsides to always storing in the cookie rather than the session. If not, we always store in the cookie. Since we've documented the current behaviour, we may however need a deprecation path involving a setting.

[msiedlarek]

I propose we discuss on this strictly on django-developers to avoid general mess and redundancy.

​http://groups.google.com/d/topic/django-developers/8THmJSioj4U/discussion

[Claude Paroz]

This ​PR tries to depart from storing the user language in the session.

[Claude Paroz]

This ​PR just adds the language in a cookie inconditionally, so we can later deprecate and remove language in the session with minimal backwards incompatibility (this was discussed on the previous PR).

[Tim Graham <timograham@…>]

In b3cd9fb1:

Refs #15902 -- Made set_language() view always set the current language in a cookie.

The plan is to later deprecate/remove storing the language in the session.

[Claude Paroz]

I updated the pull request (​https://github.com/django/django/pull/10875). I was not sure if we meant adding a deprecation in 2.2, but I guess it's late now.

[Tim Graham <timograham@…>]

In a8e2a9ba:

Refs #15902 -- Deprecated storing user's language in the session.

[Mariusz Felisiak <felisiak.mariusz@…>]

In d134b0b9:

Refs #15902 -- Stopped set_language() storing user's language in the session.

Per deprecation timeline.