I18n locale fallbacks are useful when you want your application to use translations from other locales when translations for the current locale are missing. E.g. you might want to use :en translations when translations in your applications main locale :de are missing.

To enable locale fallbacks you can simply include the Fallbacks module to the Simple backend - or whatever other backend you are using:

I18n::Backend::Simple.send(:include, I18n::Backend::Fallbacks)