I18n for model-specific Rails submit button

Those labels can be customized using I18n under the +helpers.submit+ key 
and using %{model} for translation interpolation:

  en:
    helpers:
      submit:
        create: "Create a %{model}"
        update: "Confirm changes to %{model}"

It also searches for a key specific to the given object:

  en:
    helpers:
      submit:
        post:
          create: "Add %{model}"

Source @ actionview/lib/action_view/helpers/form_helper.rb