If you need to extend or modify the config/application.rb just do it at the config/application_custom.rb file. For example if you want to change de default language to English, just add:
moduleConsul
classApplication< Rails::Application
config.i18n.default_locale =:en
config.i18n.available_locales =[:en,:es]
end
end
Remeber that in order to see this changes live you'll need to restart the server.