required by activesupport

see: https://github.com/rails/rails/blob/master/activesupport/lib/active_support/i18n.rb
version from: https://github.com/rails/rails/blob/v3.0.7/actionpack/actionpack.gemspec

twilio-rb.gemspec

@@ -10,8 +10,9 @@ Gem::Specification.new do |s|
   s.author                    = 'Stevie Graham'
   s.email                     = 'sjtgraham@mac.com'
   s.homepage                  = 'http://github.com/stevegraham/twilio-rb'
-  
+
   s.add_dependency              'activesupport', '>= 3.0.0'
+  s.add_dependency              'i18n',          '~> 0.5.0'
   s.add_dependency              'yajl-ruby',     '>= 0.7.7'
   s.add_dependency              'httparty',      '>= 0.6.1'
   s.add_dependency              'builder',       '>= 2.1.2'