i18n.rb

I18n.backend.store_translations :en, :thanks => 'Thanks %{name}!'
I18n.translate :thanks, :name => 'Jeremy'
# => 'Thanks Jeremy!'

I18n.t :missing, :default => 'Not here'
# => 'Not here'

# config/locales/en.yml
en:
  welcome: <b>welcome!</b>
  hello_html: <b>hello!</b>
  title:
    html: <b>title!</b>
 
# app/views/home/index.html.erb
<div><%= t('welcome') %></div>
<div><%= raw t('welcome') %></div>
<div><%= t('hello_html') %></div>
<div><%= t('title.html') %></div>