Use the RegionalSettings property of the SPWeb class to return an SPRegionalSettings object that represents the regional settings for a Web site. You can return the same regional settings through the SPRegionalSettings constructor. Use the RegionalSettings property of the SPUser class to return an SPRegionalSettings object that represents the regional settings for a user.
If you modify the locale of a Web site through the Locale property and call the Update method to apply changes, the following properties on the existing Web site object reflect the original regional settings, not the new ones. To retrieve the new settings, create a new Web site object, which you can do by using the OpenWeb method, to access the properties for regional settings (for example, newWebSiteObject.RegionalSettings.DateFormat).