Set application-wide own culture

App.xaml.cs

using System;
using System.Globalization;
using System.Linq;
using System.Threading;
using System.Windows;
using System.Windows.Markup;

namespace WpfApplication1
{
    /*
    In Visual Studio:
    1. Create WPF Application.
    2. Use copy-paste!
    */
    
    public partial class App
    {
        public const string CultureName = "ru-MIT";

        static App()
        {
            SetLanguage();
        }

        private static void SetLanguage()
        {
            Console.WriteLine(@">>>> SetLanguage()");
            CultureInfo culture = SystemHasMitCulture()
                ? new CultureInfo(CultureName)
                : new CultureInfo("ru-RU");

            Console.WriteLine(">>> Using culture: {0}", culture);
            Console.WriteLine(">>> Test double: {0}", 123456.789.ToString("N"));

            Thread.CurrentThread.CurrentCulture = culture;
            Thread.CurrentThread.CurrentUICulture = culture;
            CultureInfo.DefaultThreadCurrentCulture = culture;
            CultureInfo.DefaultThreadCurrentUICulture = culture;

            XmlLanguage xmlLanguage = XmlLanguage.GetLanguage(culture.IetfLanguageTag);
            FrameworkElement.LanguageProperty.OverrideMetadata(typeof (FrameworkElement),
                                                               new FrameworkPropertyMetadata(xmlLanguage));
        }

        private static bool SystemHasMitCulture()
        {
            return CultureInfo.GetCultures(CultureTypes.UserCustomCulture)
                              .Any(ci => (ci.Name == CultureName));
        }
    }
}

Program.cs

using System;
using System.Globalization;
using System.Linq;

namespace MitCultureCreator
{
    /*
    In Visual Studio:
    1. Create Console Application.
    2. Add application manifest.
    3. Uncomment following line in manifest
        <requestedExecutionLevel level="highestAvailable" uiAccess="false" />
    4. Use copy-paste!
    */
    internal class Program
    {
        private const string CultureName = "ru-MIT";
        private const string cultureEnglishName = "ru-MIT";
        private const string cultureNativeName = "Русский (Мит)";

        private static void Main(string[] args)
        {
            CreateAndRegisterOwnCulture();
        }

        private static void CreateAndRegisterOwnCulture()
        {
            var ownCulture = new CultureAndRegionInfoBuilder(CultureName, CultureAndRegionModifiers.None);

            var parentCulture = new CultureInfo("ru-RU");
            var region = new RegionInfo("RU");
            ownCulture.LoadDataFromCultureInfo(parentCulture);
            ownCulture.LoadDataFromRegionInfo(region);

            ownCulture.CultureEnglishName = cultureEnglishName;
            ownCulture.CultureNativeName = cultureNativeName;

            var nfi = (NumberFormatInfo) parentCulture.NumberFormat.Clone();
            nfi.NumberDecimalSeparator = ".";
            nfi.NumberGroupSeparator = " ";
            nfi.CurrencyDecimalSeparator = ".";
            nfi.CurrencyGroupSeparator = " ";

            ownCulture.NumberFormat = nfi;
            ownCulture.Parent = parentCulture;


            if (SystemHasMitCulture())
            {
                Console.WriteLine(">>> System already has own culture :)");
                return;
            }

            // Admin rights are needed here
            // CultureAndRegionInfoBuilder.Unregister(CultureName);

            try
            {
                // Admin rights are needed here
                Console.WriteLine(">>> Trying to set own culture");
                ownCulture.Register();
                Console.WriteLine(">>> Own culture set successfully");
            }
            catch (UnauthorizedAccessException)
            {
                Console.WriteLine(">>> Set own culture failed :(");
            }
            catch (InvalidOperationException)
            {
                Console.WriteLine(">>> Culture is already registered :)");
            }
        }

        private static bool SystemHasMitCulture()
        {
            return CultureInfo.GetCultures(CultureTypes.UserCustomCulture).Any(ci => (ci.Name == CultureName));
        }
    }
}