using System;
using System.Globalization;
using System.Threading;

class Program
{
    static void Main()
    {
        Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
        Console.WriteLine("id".Equals("ID", StringComparison.CurrentCultureIgnoreCase)); // True
        Thread.CurrentThread.CurrentCulture = new CultureInfo("tr-TR");
        Console.WriteLine("id".Equals("ID", StringComparison.CurrentCultureIgnoreCase)); // False <- bug

        Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
        Console.WriteLine("id".Equals("ID", StringComparison.OrdinalIgnoreCase)); // True
        Thread.CurrentThread.CurrentCulture = new CultureInfo("tr-TR");
        Console.WriteLine("id".Equals("ID", StringComparison.OrdinalIgnoreCase)); // True
    }
}