You can use the 't' method with `I18n.t` in models. And the first parameter of the 'add' method here should be empty string for not be reduplicate. A new method is not necessary, see the second file.

customize validation.rb

  validate :start_date_validate

  def start_date_validate
    if start_date && end_date
      if start_date >= end_date
        errors.add("", I18n.t("education_information.start_end_not_validate"))
      end
    end
  end

not need a new method.rb

  validate do
    profiles = Profile.where(:first_name => first_name, :last_name => last_name)
    unless profiles.empty?
      if self.new_record?
        errors.add("", "First name and last name already exist at the same time")
      else
        errors.add("", "First name and last name already exist at the same time") if (profiles.first.id != self.id)
      end
    end
  end