using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var dct = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase) {
		    { "english", "en"},
		    { "german", "de"},
		    { "italian", "it" }
		};
		//var url = "http://w...content-available-to-author-only...e.org/english/"; // http://e...content-available-to-author-only...e.org/
		var url = "https://w...content-available-to-author-only...e.org/German/"; // https://d...content-available-to-author-only...e.org/
		string pat = @"(?i)^(https?://)www\.(.*?)/(english|german|italian)/.*$";
		Console.WriteLine(Regex.Replace(url, pat, m => {
			    var val = "";	
			    return dct.TryGetValue(m.Groups[3].Value, out val) ?
			      $"{m.Groups[1].Value}{dct[m.Groups[3].Value]}.{m.Groups[2].Value}/" :
			      $"{m.Groups[1].Value}{m.Groups[3].Value}.{m.Groups[2].Value}/";
			  }
			)
		);
		// //http://e...content-available-to-author-only...e.org/
        	
	}
}