I would suggest you save both CultureInfo.CurrentCulture.Name
(for regional formatting) and CultureInfo.CurrentUICulture.Name
(for language) as you may want user to use one of supported application languages (e.g. en-US) and local formatting (e.g. jp-JP).
How do you restore the user settings from isolated storage? Do you assign Thread.CurrentThread.CurrentCulture
when application is initialized in App.xaml?
Moreover, you may need to assign Page.Language
from the settings (such as when a page is created, assign it as follows:
this.Lanaguage = XmlLanguage.GetLanguage(System.Threading.Thread.CurrentThread.CurrentUICulture.Name)