Allow locale to be set through the front-end

* Store the last used locale in the session
* Allow home page to be identified in helpers even when containing
  parameters
* Create initializer to explicitly set the available locales, the
  default and the load_path

app/controllers/application_controller.rb

@@ -4,7 +4,21 @@ class ApplicationController < ActionController::Base
   self.responder = ApplicationResponder
   respond_to :html
 
+  before_action :set_locale
+
   # Prevent CSRF attacks by raising an exception.
   # For APIs, you may want to use :null_session instead.
   protect_from_forgery with: :exception
+
+  private
+
+  def set_locale
+    if params[:locale] && I18n.available_locales.include?(params[:locale].to_sym)
+      session[:locale] = params[:locale]
+    end
+
+    session[:locale] ||= I18n.default_locale
+
+    I18n.locale = session[:locale]
+  end
 end

app/helpers/application_helper.rb

@@ -10,10 +10,16 @@ module ApplicationHelper
   end
 
   def home_page?
-    request.fullpath == '/'
+    # Using path because fullpath yields false negatives since it contains
+    # parameters too
+    request.path == '/'
   end
 
   def header_css
     home_page? ? '' : 'results'
   end
+
+  def available_locales_to_switch
+    I18n.available_locales - [I18n.locale]
+  end
 end

app/views/layouts/_header.html.erb

@@ -4,6 +4,14 @@
 			<div class="small-12 column">
 				<div class="right">
 					<a href="#"><%= t("layouts.header.external_link_transparency") %></a> | <a href="#"><%= t("layouts.header.external_link_opendata") %></a>
+          |
+          <span id="locale-switcher">
+            [
+              <% available_locales_to_switch.each do |locale| %>
+                <%= link_to(locale, params.merge(locale: locale), id: "locale-link-#{locale}") %>
+              <% end %>
+            ]
+          </span>
 				</div>
 			</div>
 		</div>
@@ -42,4 +50,4 @@
 			</div>
 		</div>
 	<% end %>
-</header>
+</header>

config/initializers/i18n.rb

@@ -0,0 +1,6 @@
+I18n.available_locales = [:en, :es]
+
+I18n.default_locale = :es
+
+# Add the new directories to the locales load path
+I18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}')]

spec/features/localization_spec.rb

@@ -0,0 +1,27 @@
+require 'rails_helper'
+
+feature 'Localization' do
+
+  scenario 'Wrong locale' do
+    visit root_path(locale: :es)
+    visit root_path(locale: :klingon)
+
+    expect(page).to have_text('Estamos abriendo Madrid')
+  end
+
+  scenario 'Changing locale' do
+    visit root_path(locale: :es)
+    locale_switcher = find('#locale-switcher')
+
+    expect(page).to have_text('Estamos abriendo Madrid')
+    expect(locale_switcher).to have_text('en')
+    expect(locale_switcher).to_not have_text('es')
+
+    find('#locale-link-en').click
+    locale_switcher = find('#locale-switcher')
+
+    expect(page).to have_text('We are opening Madrid')
+    expect(locale_switcher).to have_text('es')
+    expect(locale_switcher).to_not have_text('en')
+  end
+end