Merge pull request #9753 from jbarreneche/bug/render-locale-fallbacks

i18n locale fallback for localized views

actionpack/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Include I18n locale fallbacks in view lookup.
+    Fixes GH#3512.
+
+    *Juan Barreneche*
+
 *   Integration and functional tests allow headers and rack env
     variables to be passed when performing requests.
     Fixes #6513.

actionpack/lib/action_view/lookup_context.rb

@@ -43,7 +43,13 @@ def initialize_details(details)
     module Accessors #:nodoc:
     end
 
-    register_detail(:locale)  { [I18n.locale, I18n.default_locale].uniq }
+    register_detail(:locale) do
+      locales = [I18n.locale]
+      locales.concat(I18n.fallbacks[I18n.locale]) if I18n.respond_to? :fallbacks
+      locales << I18n.default_locale
+      locales.uniq!
+      locales
+    end
     register_detail(:formats) { ActionView::Base.default_formats || [:html, :text, :js, :css,  :xml, :json] }
     register_detail(:handlers){ Template::Handlers.extensions }
 

actionpack/test/controller/localized_templates_test.rb

@@ -25,4 +25,13 @@ def test_default_locale_template_is_used_when_locale_is_missing
   ensure
     I18n.locale = old_locale
   end
+
+  def test_use_fallback_locales
+    I18n.locale = :"de-AT"
+    I18n.backend.class.send(:include, I18n::Backend::Fallbacks)
+    I18n.fallbacks[:"de-AT"] = [:de]
+
+    get :hello_world
+    assert_equal "Gutten Tag", @response.body
+  end
 end