Locales in Mac OS

I adquired some day ago one Macbook Pro. I installed Rails succefully,
but now when I try to execute one project I get the next error:

macos:~/Proyectos/locambias vigosan$ rake db:migrate
(in /Users/vigosan/Proyectos/locambias)
rake aborted!
uninitialized constant Locale::System
(See full trace by running task with --trace)

Plesae, can anybody tell me how can I install locales in Mac Os?

Thanks a lot.