Add active_language controller and cookie storage

app/controllers/active_language_controller.rb

@@ -0,0 +1,10 @@
+class ActiveLanguageController < ApplicationController
+
+  def set_active_language
+    if Language.find_by_id(params[:active_language_id]) != nil
+      cookies[:active_language_id] = params[:active_language_id]
+    else
+      redirect_to root_path, status: :unprocessable_entity
+    end
+  end
+end