add a new locale using raul's translate_routes plug-in

I just started using Raul Murciano's translate_routes plug-in. It's
great. Now what I can't understand is how to add a new locale (in my
case, French). I figured that I could just add a new section to my
translation file (text.yml). I appended the following to the text.yml
file:

fr:
  back: retourner

Then in my application layout (which I copied from Raul's demo
application), I changed the code from:

<%= I18n.locale == 'es' ? link_to('en', :locale => 'en') : link_to
('es', :locale => 'es') %>

to:

<%= I18n.locale == 'fr' ? link_to('en', :locale => 'en') : link_to
('fr', :locale => 'fr') %>

When I run my application, I get this error:

No route matches {:action=>"index", :locale=>"fr"}

So, I'm guess I've got to make a change somewhere else for the
application to recognize this new route. What am I missing?