Usage IN Code,if i change the Language,the string can't change

if i have a title,
in resx, the apptitle is "app";
in the code
 public string Title
 {
     get { return GetValue<string>(); }
     set { SetValue(value); }
 }
ctor{
  Title= Translate.Key(nameof(Resources.apptitle)) + " 1.0.0";
}
in xaml 
 <TextBlock   Text="{Binding Title}"></TextBlock>
When i change the language,the Title Can't change.