I18n.reload! is only called if any of the locale files actually changed.

activesupport/lib/active_support/i18n.rb

@@ -4,5 +4,6 @@
   $stderr.puts "You don't have i18n installed in your application. Please add it to your Gemfile and run bundle install"
   raise e
 end
+
 I18n.load_path << "#{File.dirname(__FILE__)}/locale/en.yml"
 ActiveSupport.run_load_hooks(:i18n)

activesupport/lib/active_support/i18n_railtie.rb

+require "active_support"
+require "rails"
+require "active_support/file_update_checker"
+
+module I18n
+  class Railtie < Rails::Railtie
+    config.i18n = ActiveSupport::OrderedOptions.new
+    config.i18n.railties_load_path = []
+    config.i18n.load_path = []
+    config.i18n.fallbacks = ActiveSupport::OrderedOptions.new
+
+    def self.reloader
+      @reloader ||= ActiveSupport::FileUpdateChecker.new([]){ I18n.reload! }
+    end
+
+    # Add I18n::Railtie.reloader to ActionDispatch callbacks. Since, at this
+    # point, no path was added to the reloader, I18n.reload! is not triggered
+    # on to_prepare callbacks. This will only happen on the config.after_initialize
+    # callback below.
+    initializer "i18n.callbacks" do
+      ActionDispatch::Callbacks.to_prepare do
+        I18n::Railtie.reloader.execute_if_updated
+      end
+    end
+
+    # Set the i18n configuration only after initialization since a lot of
+    # configuration is still usually done in application initializers.
+    config.after_initialize do |app|
+      fallbacks = app.config.i18n.delete(:fallbacks)
+
+      app.config.i18n.each do |setting, value|
+        case setting
+        when :railties_load_path
+          app.config.i18n.load_path.unshift(*value)
+        when :load_path
+          I18n.load_path += value
+        else
+          I18n.send("#{setting}=", value)
+        end
+      end
+
+      init_fallbacks(fallbacks) if fallbacks && validate_fallbacks(fallbacks)
+
+      reloader.paths.concat I18n.load_path
+      reloader.execute_if_updated
+    end
+
+  protected
+
+    def self.include_fallbacks_module
+      I18n.backend.class.send(:include, I18n::Backend::Fallbacks)
+    end
+
+    def self.init_fallbacks(fallbacks)
+      include_fallbacks_module
+
+      args = case fallbacks
+      when ActiveSupport::OrderedOptions
+        [*(fallbacks[:defaults] || []) << fallbacks[:map]].compact
+      when Hash, Array
+        Array.wrap(fallbacks)
+      else # TrueClass
+        []
+      end
+
+      I18n.fallbacks = I18n::Locale::Fallbacks.new(*args)
+    end
+  
+    def self.validate_fallbacks(fallbacks)
+      case fallbacks
+      when ActiveSupport::OrderedOptions
+        !fallbacks.empty?
+      when TrueClass, Array, Hash
+        true
+      else
+        raise "Unexpected fallback type #{fallbacks.inspect}"
+      end
+    end
+  end
+end
\ No newline at end of file

activesupport/lib/active_support/railtie.rb

 require "active_support"
 require "rails"
+require "active_support/i18n_railtie"
 
 module ActiveSupport
   class Railtie < Rails::Railtie
@@ -26,75 +27,4 @@ class Railtie < Rails::Railtie
       Time.zone_default = zone_default
     end
   end
-end
-
-module I18n
-  class Railtie < Rails::Railtie
-    config.i18n = ActiveSupport::OrderedOptions.new
-    config.i18n.railties_load_path = []
-    config.i18n.load_path = []
-    config.i18n.fallbacks = ActiveSupport::OrderedOptions.new
-
-    initializer "i18n.initialize" do
-      ActiveSupport.on_load(:i18n) do
-        I18n.reload!
-
-        ActionDispatch::Callbacks.to_prepare do
-          I18n.reload!
-        end
-      end
-    end
-
-    # Set the i18n configuration from config.i18n but special-case for
-    # the load_path which should be appended to what's already set instead of overwritten.
-    config.after_initialize do |app|
-      fallbacks = app.config.i18n.delete(:fallbacks)
-
-      app.config.i18n.each do |setting, value|
-        case setting
-        when :railties_load_path
-          app.config.i18n.load_path.unshift(*value)
-        when :load_path
-          I18n.load_path += value
-        else
-          I18n.send("#{setting}=", value)
-        end
-      end
-
-      init_fallbacks(fallbacks) if fallbacks && validate_fallbacks(fallbacks)
-      I18n.reload!
-    end
-
-    class << self
-      protected
-
-        def init_fallbacks(fallbacks)
-          include_fallbacks_module
-          args = case fallbacks
-          when ActiveSupport::OrderedOptions
-            [*(fallbacks[:defaults] || []) << fallbacks[:map]].compact
-          when Hash, Array
-            Array.wrap(fallbacks)
-          else # TrueClass
-            []
-          end
-          I18n.fallbacks = I18n::Locale::Fallbacks.new(*args)
-        end
-
-        def include_fallbacks_module
-          I18n.backend.class.send(:include, I18n::Backend::Fallbacks)
-        end
-      
-        def validate_fallbacks(fallbacks)
-          case fallbacks
-          when ActiveSupport::OrderedOptions
-            !fallbacks.empty?
-          when TrueClass, Array, Hash
-            true
-          else
-            raise "Unexpected fallback type #{fallbacks.inspect}"
-          end
-        end
-    end
-  end
 end
\ No newline at end of file

railties/test/application/initializers/i18n_test.rb

@@ -8,48 +8,143 @@ def setup
       build_app
       boot_rails
       FileUtils.rm_rf "#{app_path}/config/environments"
+      require "rails/all"
     end
 
-    # i18n
+    def load_app
+      require "#{app_path}/config/environment"
+    end
+
+    def app
+      @app ||= Rails::Application
+    end
+
+    def assert_fallbacks(fallbacks)
+      fallbacks.each do |locale, expected|
+        actual = I18n.fallbacks[locale]
+        assert_equal expected, actual, "expected fallbacks for #{locale.inspect} to be #{expected.inspect}, but were #{actual.inspect}"
+      end
+    end
+
+    def assert_no_fallbacks
+      assert !I18n.backend.class.included_modules.include?(I18n::Backend::Fallbacks)
+    end
+
+    # Locales
     test "setting another default locale" do
       add_to_config <<-RUBY
-        config.root = "#{app_path}"
         config.i18n.default_locale = :de
       RUBY
-      require "#{app_path}/config/environment"
 
+      load_app
       assert_equal :de, I18n.default_locale
     end
 
+    # Load paths
     test "no config locales dir present should return empty load path" do
       FileUtils.rm_rf "#{app_path}/config/locales"
-      add_to_config <<-RUBY
-        config.root = "#{app_path}"
-      RUBY
-      require "#{app_path}/config/environment"
-
+      load_app
       assert_equal [], Rails.application.config.i18n.load_path
     end
 
-    test "config locales dir present should be added to load path" do
+    test "locale files should be added to the load path" do
+      app_file "config/another_locale.yml", ""
+
       add_to_config <<-RUBY
-        config.root = "#{app_path}"
+        config.i18n.load_path << config.root.join("config/another_locale.yml").to_s
       RUBY
 
-      require "#{app_path}/config/environment"
-      assert_equal ["#{app_path}/config/locales/en.yml"],  Rails.application.config.i18n.load_path
+      load_app
+      assert_equal [
+        "#{app_path}/config/locales/en.yml", "#{app_path}/config/another_locale.yml"
+      ], Rails.application.config.i18n.load_path
+
+      assert I18n.load_path.include?("#{app_path}/config/locales/en.yml")
+      assert I18n.load_path.include?("#{app_path}/config/another_locale.yml")
     end
 
-    test "config defaults should be added with config settings" do
+    test "locales are reloaded if they change between requests" do
       add_to_config <<-RUBY
-        config.root = "#{app_path}"
-        config.i18n.load_path << "my/other/locale.yml"
+        config.cache_classes = false
       RUBY
-      require "#{app_path}/config/environment"
 
-      assert_equal [
-        "#{app_path}/config/locales/en.yml", "my/other/locale.yml"
-      ], Rails.application.config.i18n.load_path
+      app_file "config/locales/en.yml", <<-YAML
+en:
+  foo: "1"
+      YAML
+
+      app_file 'config/routes.rb', <<-RUBY
+        AppTemplate::Application.routes.draw do |map|
+          match '/i18n',   :to => lambda { |env| [200, {}, [I18n.t(:foo)]] }
+        end
+      RUBY
+
+      require 'rack/test'
+      extend Rack::Test::Methods
+      load_app
+
+      get "/i18n"
+      assert_equal "1", last_response.body
+
+      app_file "config/locales/en.yml", <<-YAML
+en:
+  foo: "2"
+      YAML
+
+      get "/i18n"
+      assert_equal "2", last_response.body
+    end
+
+    # Fallbacks
+    test "not using config.i18n.fallbacks does not initialize I18n.fallbacks" do
+      I18n.backend = Class.new { include I18n::Backend::Base }.new
+      load_app
+      assert_no_fallbacks
+    end
+
+    test "config.i18n.fallbacks = true initializes I18n.fallbacks with default settings" do
+      I18n::Railtie.config.i18n.fallbacks = true
+      load_app
+      assert I18n.backend.class.included_modules.include?(I18n::Backend::Fallbacks)
+      assert_fallbacks :de => [:de, :en]
+    end
+
+    test "config.i18n.fallbacks = true initializes I18n.fallbacks with default settings even when backend changes" do
+      I18n::Railtie.config.i18n.fallbacks = true
+      I18n::Railtie.config.i18n.backend = Class.new { include I18n::Backend::Base }.new
+      load_app
+      assert I18n.backend.class.included_modules.include?(I18n::Backend::Fallbacks)
+      assert_fallbacks :de => [:de, :en]
+    end
+
+    test "config.i18n.fallbacks.defaults = [:'en-US'] initializes fallbacks with en-US as a fallback default" do
+      I18n::Railtie.config.i18n.fallbacks.defaults = [:'en-US']
+      load_app
+      assert_fallbacks :de => [:de, :'en-US', :en]
+    end
+
+    test "config.i18n.fallbacks.map = { :ca => :'es-ES' } initializes fallbacks with a mapping ca => es-ES" do
+      I18n::Railtie.config.i18n.fallbacks.map = { :ca => :'es-ES' }
+      load_app
+      assert_fallbacks :ca => [:ca, :"es-ES", :es, :en]
+    end
+
+    test "[shortcut] config.i18n.fallbacks = [:'en-US'] initializes fallbacks with en-US as a fallback default" do
+      I18n::Railtie.config.i18n.fallbacks = [:'en-US']
+      load_app
+      assert_fallbacks :de => [:de, :'en-US', :en]
+    end
+
+    test "[shortcut] config.i18n.fallbacks = [{ :ca => :'es-ES' }] initializes fallbacks with a mapping de-AT => de-DE" do
+      I18n::Railtie.config.i18n.fallbacks.map = { :ca => :'es-ES' }
+      load_app
+      assert_fallbacks :ca => [:ca, :"es-ES", :es, :en]
+    end
+
+    test "[shortcut] config.i18n.fallbacks = [:'en-US', { :ca => :'es-ES' }] initializes fallbacks with the given arguments" do
+      I18n::Railtie.config.i18n.fallbacks = [:'en-US', { :ca => :'es-ES' }]
+      load_app
+      assert_fallbacks :ca => [:ca, :"es-ES", :es, :'en-US', :en]
     end
   end
 end
\ No newline at end of file

railties/test/railties/i18n_railtie_test.rb

-require "isolation/abstract_unit"
-
-module RailtiesTest
-  class I18nRailtieTest < Test::Unit::TestCase
-    include ActiveSupport::Testing::Isolation
-
-    def setup
-      build_app
-      boot_rails
-      FileUtils.rm_rf("#{app_path}/config/environments")
-      require "rails/all"
-    end
-
-    def load_app
-      require "#{app_path}/config/environment"
-    end
-
-    def assert_fallbacks(fallbacks)
-      fallbacks.each do |locale, expected|
-        actual = I18n.fallbacks[locale]
-        assert_equal expected, actual, "expected fallbacks for #{locale.inspect} to be #{expected.inspect}, but were #{actual.inspect}"
-      end
-    end
-
-    def assert_no_fallbacks
-      assert !I18n.backend.class.included_modules.include?(I18n::Backend::Fallbacks)
-    end
-
-    test "config.i18n.load_path gets added to I18n.load_path" do
-      I18n.load_path = ['existing/path/to/locales']
-      I18n::Railtie.config.i18n.load_path = ['new/path/to/locales']
-      load_app
-
-      assert I18n.load_path.include?('existing/path/to/locales')
-      assert I18n.load_path.include?('new/path/to/locales')
-    end
-
-    test "not using config.i18n.fallbacks does not initialize I18n.fallbacks" do
-      I18n.backend = Class.new { include I18n::Backend::Base }.new
-      load_app
-      assert_no_fallbacks
-    end
-
-    test "config.i18n.fallbacks = true initializes I18n.fallbacks with default settings" do
-      I18n::Railtie.config.i18n.fallbacks = true
-      load_app
-      assert I18n.backend.class.included_modules.include?(I18n::Backend::Fallbacks)
-      assert_fallbacks :de => [:de, :en]
-    end
-
-    test "config.i18n.fallbacks = true initializes I18n.fallbacks with default settings even when backend changes" do
-      I18n::Railtie.config.i18n.fallbacks = true
-      I18n::Railtie.config.i18n.backend = Class.new { include I18n::Backend::Base }.new
-      load_app
-      assert I18n.backend.class.included_modules.include?(I18n::Backend::Fallbacks)
-      assert_fallbacks :de => [:de, :en]
-    end
-
-    test "config.i18n.fallbacks.defaults = [:'en-US'] initializes fallbacks with en-US as a fallback default" do
-      I18n::Railtie.config.i18n.fallbacks.defaults = [:'en-US']
-      load_app
-      assert_fallbacks :de => [:de, :'en-US', :en]
-    end
-
-    test "config.i18n.fallbacks.map = { :ca => :'es-ES' } initializes fallbacks with a mapping ca => es-ES" do
-      I18n::Railtie.config.i18n.fallbacks.map = { :ca => :'es-ES' }
-      load_app
-      assert_fallbacks :ca => [:ca, :"es-ES", :es, :en]
-    end
-
-    test "[shortcut] config.i18n.fallbacks = [:'en-US'] initializes fallbacks with en-US as a fallback default" do
-      I18n::Railtie.config.i18n.fallbacks = [:'en-US']
-      load_app
-      assert_fallbacks :de => [:de, :'en-US', :en]
-    end
-
-    test "[shortcut] config.i18n.fallbacks = [{ :ca => :'es-ES' }] initializes fallbacks with a mapping de-AT => de-DE" do
-      I18n::Railtie.config.i18n.fallbacks.map = { :ca => :'es-ES' }
-      load_app
-      assert_fallbacks :ca => [:ca, :"es-ES", :es, :en]
-    end
-
-    test "[shortcut] config.i18n.fallbacks = [:'en-US', { :ca => :'es-ES' }] initializes fallbacks with the given arguments" do
-      I18n::Railtie.config.i18n.fallbacks = [:'en-US', { :ca => :'es-ES' }]
-      load_app
-      assert_fallbacks :ca => [:ca, :"es-ES", :es, :'en-US', :en]
-    end
-  end
-end
\ No newline at end of file