rovarspraket.rb

#!/usr/bin/env ruby

VOWELS     = "AEIOUYÅÄÖ"
CONSONANTS = ('A'..'Z').reject { |char| VOWELS.include? char }

def consonant? char
  CONSONANTS.include? char or CONSONANTS.include? char.upcase
end

def rovarspraket string
  string.each_char.map do |char|
    if consonant? char
      char + 'o' + char.downcase
    else
      char
    end
  end.join
end

INPUT_1  = "Jag talar Rövarspråket!"
OUTPUT_1 = "Jojagog totalolaror Rorövovarorsospoproråkoketot!"

INPUT_2  = "I'm speaking Robber's language!"
OUTPUT_2 = "I'mom sospopeakokinongog Rorobobboberor'sos lolanongoguagoge!"

throw "Input 1 failed." unless rovarspraket(INPUT_1) == OUTPUT_1
throw "Input 2 failed." unless rovarspraket(INPUT_2) == OUTPUT_2