Add a language selector

[Aleksej]

Please add a way to change UI language, overriding Accept-Language.
E.g. a drop-down and/or an URL piece.

[Christopher Allan Webber]

It's hard to think of a good place to put this. But one easy place
for now is in user preferences. Yes, it requires you to be logged
in. But at least it's one option besides browser defaults until/if
someone finds a nicer place UI-wise for it to be. And we should
have user-level preference on language settings anyway.

[Christopher Allan Webber]

Jef, do you think adding a language dropdown in the user profile
editor would be an appropriate solution for now?

[Christopher Allan Webber]

By the way... I forgot that I added this feature, but for quick
"testing" of pages, you can do:

`http://omgmg.dyndns.org:6543/auth/login/?lang=eo <http://omgmg.dyndns.org:6543/auth/login/?lang=eo>`_

?lang=lang\_code

It won't stay persistent, but might help while debugging, or
linking a specific page with a specific language.

[Will Kahn-Greene]

The original url for this bug was ​http://bugs.foocorp.net/issues/578 .

[spaetz]

Hi, the backend work for this is all in. We will display languages in this order:

1) ?lang=ru parameter (either GET or POST)
2) use the "target_lang" variable in the session object (which is never set so far)
3) based on browser preference

So we clearly need to improve case 2), so that a user can set a preferred language in her account settings.

[Aleksej]

Wikimedia Commons shows the language with ?uselang=, but keeps it between pages using something else (for a logged-out user).

[Emily O'Leary]

Having a language preference for logged in users would be really helpful for making sure that any communications sent to those users are in their preferred language (see #504). I could see this have both of those implementations.

Adding it as a field for when someone registers would also be helpful.