Add a site setting to allow users to toggle I18n.locale

It is false by default.

app/assets/javascripts/discourse/controllers/preferences_controller.js

@@ -11,6 +11,10 @@ Discourse.PreferencesController = Discourse.ObjectController.extend({
     return Discourse.SiteSettings.allow_uploaded_avatars;
   }.property(),
 
+  allowUserLocale: function() {
+    return Discourse.SiteSettings.allow_user_locale;
+  }.property(),
+
   // By default we haven't saved anything
   saved: false,
 

app/assets/javascripts/discourse/templates/user/preferences.js.handlebars

@@ -66,6 +66,7 @@
       </div>
     </div>
 
+    {{#if allowUserLocale}}
       <div class="control-group">
         <label class="control-label">{{i18n user.locale.title}}</label>
         <div class="controls">
@@ -75,6 +76,7 @@
           {{i18n user.locale.instructions}}
         </div>
       </div>
+    {{/if}}
 
     <div class="control-group">
       <label class="control-label">{{i18n user.bio}}</label>

app/controllers/application_controller.rb

@@ -109,7 +109,7 @@ class ApplicationController < ActionController::Base
   end
 
   def set_locale
-    I18n.locale = if current_user && current_user.locale.present?
+    I18n.locale = if SiteSetting.allow_user_locale && current_user && current_user.locale.present?
                     current_user.locale
                   else
                     SiteSetting.default_locale

config/locales/server.en.yml

@@ -549,6 +549,7 @@ en:
 
   site_settings:
     default_locale: "The default language of this Discourse instance (ISO 639-1 Code)"
+    allow_user_locale: "Allow users to choose their own language interface preference"
     min_post_length: "Minimum post length in characters"
     min_private_message_post_length: "Minimum post length in characters for private messages"
     max_post_length: "Maximum post length in characters"

config/locales/server.fr.yml

@@ -484,6 +484,7 @@ fr:
       description: "HTML qui sera ajouté au pied de toutes les pages"
   site_settings:
     default_locale: "Le langage par défaut de cette instance de Discourse (code ISO 639-1)"
+    allow_user_locale: "Permettre aux utilisateurs de choisir leur propre préférence de langue pour l'interface"
     min_post_length: "Longueur minimale des messages en nombre de caractères"
     min_private_message_post_length: "Longueur minimale des messages privés en nombre de caractères"
     max_post_length: "Longueur maximale des messages en nombres de caractères"

config/site_settings.yml

@@ -24,6 +24,9 @@ basic:
   default_locale:
     default: 'en'
     enum: 'LocaleSiteSetting'
+  allow_user_locale:
+    client: true
+    default: false
   ga_tracking_code:
     client: true
     default: ''

spec/controllers/application_controller_spec.rb

@@ -55,6 +55,15 @@ describe TopicsController do
 
       I18n.locale.should == :fr
     end
+
+    it 'is sets the default locale when the setting not enabled' do
+      user = Fabricate(:user, locale: :fr)
+      log_in_user(user)
+
+      get :show, {topic_id: topic.id}
+
+      I18n.locale.should == :en
+    end
   end
 
 end