using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var car = "A test: んつきゃきゅきょ";
		Console.WriteLine(car);
		car = car.RegexReplace ( "ん", "n" )
		    .RegexReplace ( "つ", "tsu" )
		    .RegexReplace ( "きゃ", "kya" )
		    .RegexReplace ( "きゅ", "kyu" )
		    .RegexReplace ( "きょ", "kyo" );
 
		Console.WriteLine(car);
	}
}
 
public static class RegexStringExtension
{
    public static String RegexReplace ( this String haystack, String regex, String replacement )
    {
        return new Regex ( regex ).Replace ( haystack, replacement );
    }
}
 

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