The translated model name, translated attribute name, and value are always available for interpolation as model, attribute and value respectively.

So, for example, instead of the default error message “cannot be blank” you could use the attribute name like this: "Please fill in your %{attribute}".

count, where available, can be used for pluralization if present

Source: Rails Internationalization (I18n) API - Ruby on Rails Guides

I find that not everyone knows this, so I thought I’d share.