i18n Pluralization

Try this:

en.yml :

en:
  misc:
    kids:
      zero: no kids
      one: 1 kid
      other: %{count} kids

In a view:

You have <%= t('misc.kids', :count => 4) %>

Updated answer for languages with multiple pluralization (tested with Rails 3.0.7):

File config/initializers/pluralization.rb:

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

File config/locales/plurals.rb:

{:ru => 
  { :i18n => 
    { :plural => 
      { :keys => [:one, :few, :other],
        :rule => lambda { |n| 
          if n == 1
            :one
          else
            if [2, 3, 4].include?(n % 10) && 
               ![12, 13, 14].include?(n % 100) && 
               ![22, 23, 24].include?(n % 100)

              :few 
            else
              :other 
            end
          end
        } 
      } 
    } 
  } 
}

#More rules in this file: https://github.com/svenfuchs/i18n/blob/master/test/test_data/locales/plurals.rb
#(copy the file into `config/locales`)

File config/locales/en.yml:

en:
  kids:
    zero: en_zero
    one: en_one
    other: en_other

File config/locales/ru.yml:

ru:
  kids:
    zero: ru_zero
    one: ru_one
    few: ru_few
    other: ru_other

Test:

$ rails c
>> I18n.translate :kids, :count => 1
=> "en_one"
>> I18n.translate :kids, :count => 3
=> "en_other"
>> I18n.locale = :ru
=> :ru
>> I18n.translate :kids, :count => 1
=> "ru_one"
>> I18n.translate :kids, :count => 3
=> "ru_few"  #works! yay! 
>> I18n.translate :kids, :count => 5
=> "ru_other"  #works! yay!