gistfile1.txt

# Framework Object::say_hello
class Object
  def say_hello
    "hello"
  end
end

# Your Object class
class Object
  module InSpanish
    def say_hello
      "hola"
    end
  end
  include InSpanish
  
  module InEnglish
    expects_method = Object.instance_method(:say_hello)
    define_method :say_hello do |*args|
      expects_method.bind(self).call(*args)
    end
  end
  include InEnglish

  def say_hello
    (@language || InEnglish).instance_method(:say_hello).bind(self).call
  end
  
  def in_english(&block)
    @language = InEnglish
    instance_eval(&block)
  end
  
  def in_spanish(&block)
    @language = InSpanish
    instance_eval(&block)
  end
end

in_english do
  say_hello # => "hello"
end

in_spanish do
  say_hello # => "hola"
end