I found out using i18n with django breaks caching completely.
(reverse proxy & browser caching, that is).

Initially I filed a bug about this [1], But its more complicated that
just a bug.  Therefor I post the topic here.

Whats the problem:
enabling django.middleware.locale.LocaleMiddleware,   makes your
complete site un-cachable, as _every_ response   gets automatically
the following http header  "Vary: Cookie"
(as LocaleMiddleware reads the session -> session.accessed becomes
True -> Vary: Cookie gets added).

"Vary: Cookie"   effectively  means, with all current browsers, that
the browser will not, never cache the page.
As discussed in [1], there is nothing you can do on views that
actually user i18n. They really do vary on the cookie.

Unfortunately, this happens for _every_ view, also the views that do
_not_ have anything to do with translations.

So I'm wondering if we can improve django locale handling, so that
only views that matter from an i18n point-of-view, get the "Vary:
Cookie" header.

some thoughts:
a) Make LocaleMiddleware configurable, which urls are i18n enabled and
which not.  (but include/exclude patterns.
b) can we somehow make the reading of the session by LocaleMiddleware
so lazy, that only
when translation kicks in we touch the session.

Any thoughts?

Regards,
Harm

[1] http://code.djangoproject.com/ticket/13217