Ruby on Rails 3.2 Mailer, localize mail subject field - ruby-on-rails-3

Question

I'm currently writing a mailer in RoR 3.2 that would send out mails that should be localized based on a users' language. I managed to render the correct localized views but I'm having some difficulties with some fields that require changing the locale (like the subject).
I've already read some posts that are against changing the locale before sending the email. The users have many different languages and that would mean changing my locale every time a user is sent an email.
I know that it would be possible to change the locale, send the email, change back the locale. This doesn't feel like the rails way. Is there a correct way of doing this?
Here's a snippet:
class AuthMailer < ActionMailer::Base
add_template_helper(ApplicationHelper)
default :from => PREDEF_MAIL_ADDRESSES::System[:general]
[...]
def invite(address, token, locale)
#token = token
#locale = locale
#url = url_for(:controller => "signup_requests", :action => "new", :token => token.key, :locale => locale)
mail(:subject => "Invitation", :to => address) do |format|
format.html { render ("invite."+locale) }
format.text { render ("invite."+locale) }
end
end
[...]
end
My views
auth_mailer
invite.en.html.erb
invite.en.text.erb
invite.it.html.erb
invite.it.text.erb
...
In short, in this case, I'd like to localize the :subject using the #locale, but not by running: I18n.locale = locale

Answer 1

It is OK to change the global locale temporarily. There is a handy I18n.with_locale method for that. Also ActionMailer automatically translates a subject.
class AuthMailer
def invite(address, token, locale)
#token = token
#locale = locale
#url = url_for(:controller => "signup_requests", :action => "new", :token => token.key, :locale => locale)
I18n.with_locale(locale) do
mail(:to => address)
end
end
end
In the locale:
en:
auth_mailer:
invite:
subject: Invitation

Answer 2

Rails 4 way:
# config/locales/en.yml
en:
user_mailer:
welcome:
subject: 'Hello, %{username}'
# app/mailers/user_mailer.rb
class UserMailer < ActionMailer::Base
def welcome(user)
mail(subject: default_i18n_subject(username: user.name))
end
end
default_i18n_subject - Translates the subject using Rails I18n class under [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. If the subject has interpolations, you can pass them through the interpolations parameter.

Answer 3

You should be able to pass a locale when you call I18n like so:
mail(:subject => I18n.t("app.invite.subject", :locale => locale), :to => address) do |format|
format.html { render ("invite."+locale) }
format.text { render ("invite."+locale) }
end
Remember that the locale variable needs to be a symbol.