Reorder i18n hooks and reword comments

If eager loading is enabled, `before_eager_load` runs
before `after_initialize`. I believe it is natural to
define these hooks matching that order.

For this to make sense, it is important to highlight
that initialize_i18n is idempotent.

Author: fxn

activesupport/lib/active_support/i18n_railtie.rb

@@ -14,15 +14,18 @@ class Railtie < Rails::Railtie
 
     config.eager_load_namespaces << I18n
 
-    # Set the i18n configuration after initialization since a lot of
-    # configuration is still usually done in application initializers.
-    config.after_initialize do |app|
+    # Make sure i18n is ready before eager loading, in case any eager loaded
+    # code needs it.
+    config.before_eager_load do |app|
       I18n::Railtie.initialize_i18n(app)
     end
 
-    # Trigger i18n config before any eager loading has happened
-    # so it's ready if any classes require it when eager loaded.
-    config.before_eager_load do |app|
+    # i18n initialization needs to run after application initialization, since
+    # initializers may configure i18n.
+    #
+    # If the application eager loaded, this was done on before_eager_load. The
+    # hook is still OK, though, because initialize_i18n is idempotent.
+    config.after_initialize do |app|
       I18n::Railtie.initialize_i18n(app)
     end