localization_helper.rb

# Helpery pożyczone z projektu 'russian'
module LocalizationHelper
  # Ułatwia wypisywanie komunikatów zależnych od wartości liczbowych
  #
  # Użycie: 
  #   pluralize(1, "piłka", "piłki", "piłek")               # => "piłka"
  #   pluralize(2, "piłka", "piłki", "piłek")               # => "piłki"
  #   pluralize(21, "piłka", "piłki", "piłek")              # => "piłek"
  #   pluralize(4.12, "piłka", "piłki", "piłek", "piłki")   # => "piłki"
  #   pluralize(200, "# but", "# buty", "# butów")          # => "200 butów"
  def pluralize(n, *variants)
    raise ArgumentError, "Must have a Numeric as a first parameter" unless n.is_a?(Numeric)
    raise ArgumentError, "Must have at least 3 variants for pluralization" if variants.size < 3
    raise ArgumentError, "Must have at least 4 variants for pluralization" if (variants.size < 4 && n != n.round)
    variants_hash = pluralization_variants_to_hash(n, *variants)
    I18n.backend.send(:pluralize, I18n.locale, variants_hash, n)
  end
  alias :p :pluralize

protected

  # Converts an array of pluralization variants to a Hash that can be used
  # with I18n pluralization.
  def pluralization_variants_to_hash(n, *variants)
    {
      :one => variants[0].gsub(/#/, n.to_s),
      :few => variants[1].gsub(/#/, n.to_s),
      :many => variants[2].gsub(/#/, n.to_s),
      :other => variants[3] && variants[3].gsub(/#/, n).to_s
    }
  end

end

pl-pluralization.rb

# Reguły wzorowane na http://github.com/yaroslav/russian (dla polskiego są prostsze)
# Polski:
#   :one    = 1
#   :few    = 2-4, 22-24, 32-34...
#   :many   = 0, 5-21, 25-31, 35-41...
#   :other  = pozostałe (np. 0.5, 3.14)

{
  :pl => {
    :i18n => {
      :pluralize => lambda { |n| 
        n == 1 ? :one : [2, 3, 4].include?(n % 10) && ![12, 13, 14].include?(n % 100) ? :few : n % 10 == 0 || [1, 5, 6, 7, 8, 9].include?(n % 10) || [11, 12, 13, 14].include?(n % 100) ? :many : :other 
      }
    }
  }
}

pluralization.rb

require 'i18n/backend/pluralization'
I18n::Backend::Simple.send(:include, I18n::Backend::Pluralization)

show.html.erb

<%= pluralize(room.size, "# osoby", "# osób", "# osób") %>
<%= pluralize(room.windows_count, "# okno", "# okna", "# okien") %>