Here it is: http://guides.rubyonrails.org/i18n.html#translations-for-active-record-models
Basically you do Model.model_name.human or model_instance.class.model_name.human
It appears this is the same as class.demodulize.underscore.humanize based on the initializer here:
http://api.rubyonrails.org/classes/ActiveModel/Name.html
So it is missing the titlecase bit.