first step

Billing.Shared/UI/Definition.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Threading.Tasks;
 using System.Xml.Linq;
+using Billing.Languages;
 using Billing.Models;
 using Xamarin.Forms;
 
@@ -77,6 +79,11 @@ namespace Billing.UI
             Grid.SetRowSpan(view, rowSpan);
             return view;
         }
+
+        public static async Task ShowMessage(this Page page, string message, string title = null)
+        {
+            await page.DisplayAlert(title ?? page.Title, message, Resource.Ok);
+        }
     }
 
     public static class ModelExtensionHelper