Added warning for reserved YAML keywords.

Update i18n.md

Addressed Feedback

guides/source/i18n.md

@@ -409,6 +409,35 @@ NOTE: You need to restart the server when you add new locale files.
 
 You may use YAML (`.yml`) or plain Ruby (`.rb`) files for storing your translations in SimpleStore. YAML is the preferred option among Rails developers. However, it has one big disadvantage. YAML is very sensitive to whitespace and special characters, so the application may not load your dictionary properly. Ruby files will crash your application on first request, so you may easily find what's wrong. (If you encounter any "weird issues" with YAML dictionaries, try putting the relevant portion of your dictionary into a Ruby file.)
 
+If your translations are stored in YAML files, certain keys must be escaped. They are:
+
+* true, on, yes
+* false, off, no
+
+Examples:
+
+```erb
+# confing/locales/en.yml
+en:
+  success:
+    'true':  'True!'
+    'on':    'On!'
+    'false': 'False!'
+  failure:
+    true:    'True!'
+    off:     'Off!'
+    false:   'False!'
+```
+
+```ruby
+I18n.t 'success.true' # => 'True!'
+I18n.t 'success.on' # => 'On!'
+I18n.t 'success.false' # => 'False!'
+I18n.t 'failure.false' # => Translation Missing
+I18n.t 'failure.off' # => Translation Missing
+I18n.t 'failure.true' # => Translation Missing
+```
+
 ### Passing Variables to Translations
 
 One key consideration for successfully internationalizing an application is to

railties/lib/rails/generators/rails/app/templates/config/locales/en.yml

@@ -16,6 +16,16 @@
 #
 # This would use the information in config/locales/es.yml.
 #
+# The following keys must be escaped otherwise they will not be retrieved by
+# the default I18n backend:
+#
+# true, false, on, off, yes, no
+#
+# Instead, surround them with single quotes.
+#
+# en:
+#   'true': 'foo'
+#
 # To learn more, please read the Rails Internationalization guide
 # available at http://guides.rubyonrails.org/i18n.html.