default_i18n_subject()
Translates the subject using Rails I18n class under [:actionmailer, mailer_scope, action_name] scope. If it does not find a translation for the subject under the specified scope it will default to a humanized version of the action_name.
# File actionmailer/lib/action_mailer/base.rb, line 674 def default_i18n_subject #:nodoc: mailer_scope = self.class.mailer_name.gsub('/', '.') I18n.t(:subject, :scope => [mailer_scope, action_name], :default => action_name.humanize) end