Fixes #16758: Create language cookie if required

[m2martin]

Fixes: #16758

If a new browser session has no language cookie set, check if it should be set and redirect to the requested page.

[m2martin]

I'd like to get rid of the redirection, but django.utils.translation.activate() seems worthless here. Does someone have a better idea?

[jeremystretch]

This probably isn't the best approach to ensure translation is active. Instead, we should update the calls to set_cookie() in LoginView and UserConfigView to set an expiration time on the language cookie (which should presumably match the expiration time of the session cookie, which was derived from LOGIN_TIMEOUT).

[m2martin]

I totally agree that this approach is not very elegant. After looking into the way how Django handles cookie renewals, I found a very simple way to accomplish the same for our language cookie. Please have a look at the new commit.

[dreng]

IMO, instead of dealing with cookies, those kind of user preferences should be stored in the database. Otherwise you will have to set the language preference in every browser on every computer again (not even mentioning private browsing). In our case you have to set it each day actually, because cookies will be automatically removed by a group policy. That can be really annoying.

[jeremystretch]

Thanks @m2martin, great work!