feat(i18n): enable localization by query param

Providing a query param ("locale") will enable localization. A language picker will be shown once
localization is activated. Locale is stored in a cookie "locale".

app/controllers/application_controller.rb

@@ -21,7 +21,7 @@ class ApplicationController < ActionController::Base
   around_action :switch_locale
 
   helper_method :multiple_devise_profile_connect?, :instructeur_signed_in?, :current_instructeur, :current_expert, :expert_signed_in?,
-    :administrateur_signed_in?, :current_administrateur, :current_account
+    :administrateur_signed_in?, :current_administrateur, :current_account, :localization_enabled?, :set_locale
 
   def staging_authenticate
     if StagingAuthService.enabled? && !authenticate_with_http_basic { |username, password| StagingAuthService.authenticate(username, password) }
@@ -71,6 +71,17 @@ class ApplicationController < ActionController::Base
 
   alias_method :pundit_user, :current_account
 
+  def localization_enabled?
+    ENV.fetch('LOCALIZATION_ENABLED', 'false') == 'true' || cookies[:locale].present?
+  end
+
+  def set_locale(locale)
+    if locale && locale.to_sym.in?(I18n.available_locales)
+      cookies[:locale] = locale
+      locale
+    end
+  end
+
   protected
 
   def feature_enabled?(feature_name)
@@ -309,14 +320,25 @@ class ApplicationController < ActionController::Base
   end
 
   def switch_locale(&action)
-    locale = nil
+    locale = extract_locale_from_query_params ||
-    if cookies[:locale]
+      extract_locale_from_cookie ||
-      locale = cookies[:locale]
+      extract_locale_from_accept_language_header ||
-    elsif ENV.fetch('LOCALIZATION_ENABLED', 'false') == 'true'
+      I18n.default_locale
-      locale = http_accept_language.compatible_language_from(I18n.available_locales)
+
-    else
-      locale = I18n.default_locale
-    end
     I18n.with_locale(locale, &action)
   end
+
+  def extract_locale_from_query_params
+    set_locale(request.query_parameters[:locale])
+  end
+
+  def extract_locale_from_cookie
+    cookies[:locale]
+  end
+
+  def extract_locale_from_accept_language_header
+    if localization_enabled?
+      http_accept_language.compatible_language_from(I18n.available_locales)
+    end
+  end
 end

app/controllers/root_controller.rb

@@ -89,7 +89,7 @@ class RootController < ApplicationController
   end
 
   def save_locale
-    cookies[:locale] = params[:locale]
+    set_locale(params[:locale])
-    redirect_to request.referer
+    redirect_back(fallback_location: root_path)
   end
 end

app/views/layouts/_header.haml

@@ -82,6 +82,6 @@
         - else
           = render partial: 'shared/help/help_button'
 
-      - if ENV.fetch('LOCALIZATION_ENABLED', 'false') == 'true'
+      - if localization_enabled?
         %li
           = render partial: 'layouts/locale_dropdown'

app/views/layouts/_locale_dropdown.html.haml

@@ -1,11 +1,11 @@
-.dropdown.locale-dropdown
+.dropdown.locale-dropdown.header-menu-opener
-  %button.button.dropdown-button.icon-only.header-menu-button{ title: "Translate", 'aria-expanded' => 'false', 'aria-controls' => 'locale_menu' }
+  %button.button.dropdown-button.icon-only.header-menu-button{ title: "Translate", aria: { expanded: 'false', controls: 'locale_menu' } }
     .hidden Translate
-    = image_tag "icons/translate-icon.svg", alt: 'Translate', 'aria-hidden':'true'
+    = image_tag "icons/translate-icon.svg", alt: 'Translate', width: 24, height: 24, lazy: true, aria: { hidden: true }
   %ul.header-menu.dropdown-content
     %li
       = link_to save_locale_path(locale: :en), method: :post, class: "menu-item menu-link" do
-      EN - English
+        EN – English
     %li
       = link_to save_locale_path(locale: :fr), method: :post, class: "menu-item menu-link" do
-      FR - français
+        FR – français

spec/features/i18n_spec.rb

@@ -8,7 +8,7 @@ feature 'Accessing the website in different languages:' do
       expect(page).to have_text('Connectez-vous')
 
       click_on 'Translate'
-      click_on 'EN - English'
+      click_on 'EN – English'
 
       # The page is now in English
       expect(page).to have_text('Sign in')

spec/views/layouts/_header_spec.rb

@@ -5,6 +5,7 @@ describe 'layouts/_header.html.haml', type: :view do
     allow(view).to receive(:multiple_devise_profile_connect?).and_return(false)
     allow(view).to receive(:instructeur_signed_in?).and_return((profile == :instructeur))
     allow(view).to receive(:current_instructeur).and_return(current_instructeur)
+    allow(view).to receive(:localization_enabled?).and_return(false)
 
     if user
       sign_in user

spec/views/layouts/procedure_context.html.haml_spec.rb

@@ -5,6 +5,7 @@ describe 'layouts/procedure_context.html.haml', type: :view do
   before do
     allow(view).to receive(:instructeur_signed_in?).and_return(false)
     allow(view).to receive(:administrateur_signed_in?).and_return(false)
+    allow(view).to receive(:localization_enabled?).and_return(false)
   end
 
   subject do