Which are the steps to make Locale language switcher block appear at selected area? After this question on which module to use to handle interface translation I was expecting the setup of Locale to be pretty straightforward. I guess it is not.  

Well, my backend and navigation menus got translated right away but the main objective (as you can see by reading the other question) was to allow any user to change language as needed.

So the goal is to setup the language switcher block in order that it is available to everyone.
Steps performed:


Enable module Locale
Setup language switcher block to appear at some area
Configured block to appear to all roles on every page
Added a new language and imported the .po file
Checked all locale permissions (except anonymous user -> translation)


Am I missing something?
You need to set the language negotiation.