What's a relatively fast way of checking if a string is decrypted English?
Searching purley for substrings in a string would be a programming question but since Stackoverflow already sent you here I will give it a try:

Java:

public class MyClass
{
    public static void main(String[] args)
    {
        String myString = "XPAWWALLTPJZYYZWBGSHGARECPVHDAAPLJLBGAPVTFVCWAS";

        int intIndex = myString.indexOf("ARE");

        if(intIndex == - 1)
        {
            System.out.println("ARE was not found");
        }
        else
        {
            System.out.println("Found ARE at index "+ intIndex);
        }
    }
}


C#:

using System;

public class MyClass
{
   public static void Main()
   {
      string myString = "XPAWWALLTPJZYYZWBGSHGARECPVHDAAPLJLBGAPVTFVCWAS";

      if (myString.Contains("ARE") == true)
      {
         Console.WriteLine("Found ARE");
      }
      else
      {
         Console.WriteLine("Word ARE was not found!");
      }
   }
}


These should both work.

You can then create a loop that searches the string for common words.