Page 229 gives the example that if the Spanish language (es) is requested, you should get an error such as “es translation not available”.
Unfortunately, I cannot reproduce this behaviour, except by entering an invented language (e.g. “zz”) in the URL.
If, for example, I enter a valid nation code (e.g. “it”), I get no error.
I also wonder why I should get an error with the Spanish language: has this not been declared in the config/initialisers/i18n.rb file?