Recently i have been using CultureAndRegionInfoBuilder class to create custom cultures in .NET.
With CultureAndRegionInfoBuilder class you can define a custom culture that is new or based on an existing culture and region. You can specify the culture and region information for example the associated language, sublanguage, country/region, calendar, and cultural conventions to great detail by using specific CultureInfo and RegionInfo classes. The custom culture can also be installed on a computer and subsequently used by any application running on that computer.
I highly recommend using this feature in .NET to create custom cultures for the application.