Formula pluralization for I18n

localization_backend.rb

# Formula pluralizations for I18n 
# by Wojciech Zieliński (zielinskiwojciech@gmail.com, http://github.com/baael)

module I18n
  module Backend
  class FormulaPluralization < Simple
     def pluralize(locale, entry, count)
     return entry unless entry.is_a?(Hash) and count
     case translations[locale][:formula].nil?
    when false
      formulas=translations[locale][:formula].dup
      key=formulas.delete(:default).to_sym
      formulas.each { |formula|
        key = formula[0].to_sym if eval(formula[1].gsub(/(\\\\)?\{\{([^\}]+)\}\}/,count.to_s))
      }
    else
      key = :zero if count == 0 && entry.has_key?(:zero)
      key ||= count == 1 ? :one : :other
     end
     raise InvalidPluralizationData.new(entry, count) unless entry.has_key?(key)
     entry[key]
     end
  end
  end
end
I18n.backend = I18n::Backend::FormulaPluralization .new

pl.yml

# Formula pluralizations for I18n 
# by Wojciech Zieliński (zielinskiwojciech@gmail.com, http://github.com/baael)

pl:
  formula:
    one: "{{count}}==1 && {{count}}%100!=11"
    few: "(2..4).include?({{count}}%10) && !(12..14).include?({{count}}%100)"
    default: "other"
  test:
    gry:
     one: "gra"
     few: "gry"
     other: "gier"

tests

 I18n.t("test.gry", :count => 0 ).should == "gier"
 I18n.t("test.gry", :count => 1 ).should == "gra"
 I18n.t("test.gry", :count => 2 ).should == "gry"
 I18n.t("test.gry", :count => 3 ).should == "gry"
 I18n.t("test.gry", :count => 4 ).should == "gry"
 I18n.t("test.gry", :count => 5 ).should == "gier"
 I18n.t("test.gry", :count => 6 ).should == "gier"
 I18n.t("test.gry", :count => 7 ).should == "gier"
 I18n.t("test.gry", :count => 21).should == "gier"
 I18n.t("test.gry", :count => 22).should == "gry"
 I18n.t("test.gry", :count => 25).should == "gier"
 I18n.t("test.gry", :count => 26).should == "gier"
 I18n.t("test.gry", :count => 101).should == "gier"