SetDefaultCulture.cs

public void SetDefaultCulture(CultureInfo culture)
{
    Type type = typeof(CultureInfo);
 
    try
    {
        type.InvokeMember("s_userDefaultCulture",
                            BindingFlags.SetField | BindingFlags.NonPublic | BindingFlags.Static,
                            null,
                            culture,
                            new object[] { culture });
 
        type.InvokeMember("s_userDefaultUICulture",
                            BindingFlags.SetField | BindingFlags.NonPublic | BindingFlags.Static,
                            null,
                            culture,
                            new object[] { culture });
    }
    catch { }
 
    try
    {
        type.InvokeMember("m_userDefaultCulture",
                            BindingFlags.SetField | BindingFlags.NonPublic | BindingFlags.Static,
                            null,
                            culture,
                            new object[] { culture });
 
        type.InvokeMember("m_userDefaultUICulture",
                            BindingFlags.SetField | BindingFlags.NonPublic | BindingFlags.Static,
                            null,
                            culture,
                            new object[] { culture });
    }
    catch { }
}