Adding translations in the String in Rails

I am new to rai开发者_如何学Gols.. I am having a line in the mailing queue.rb file as

subject ="Mail : Welcome to app"

I have added translation for Welcome to app as

        str_welcome: "Welcome to app"

Now i am trying to replace Welcome to app in the file with the str_welcome

how to do that as i have another prefix ("Mail") also ..

Use the i18N inside Rails

subject = i18N.t('str_welcome')

All about i18n in rails : http://guides.rubyonrails.org/i18n.html