string word = Console.ReadLine().ToLower();

switch (word)
{
    case "cat":
    case "katze":
        Console.WriteLine("cat - Katze");
        break;
    case "dog":
    case "hund":
        Console.WriteLine("dog - Hund");
        break;
    case "house":
    case "haus":
        Console.WriteLine("house - Haus");
        break;
    case "flower":
    case "blume":
        Console.WriteLine("flower - Blume");
        break;
    case "chair":
    case "stuhl":
        Console.WriteLine("chair - Stuhl");
        break;
    case "apple":
    case "apfel":
        Console.WriteLine("apple - Apfel");
        break;
    default:
        Console.WriteLine("Word not known in the dictionary.");
        break;
}

Console.ReadKey();