use this as a helper method.

conditional_html.html.haml

def conditional_html(options={}, &blk)
  attrs = options.map { |(k, v)| " #{h k}=\"#{h v}\"" }.join('')
  [ "<!--[if lt IE 7 ]>                <html#{attrs} class=\"ie6 no-js oldie\"> <![endif]-->",
    "<!--[if IEMobile 7 ]>             <html#{attrs} class=\"iemob7 no-js oldie\"> <![endif]-->",
    "<!--[if (IE 7) & !(IEMobile 7) ]> <html#{attrs} class=\"ie7 no-js oldie\"> <![endif]-->",
    "<!--[if IE 8 ]>                   <html#{attrs} class=\"ie8 no-js oldie\"> <![endif]-->",
    "<!--[if IE 9 ]>                   <html#{attrs} class=\"ie9 no-js oldie\"> <![endif]-->",
    "<!--[if (gt IE 9)|!(IE)]><!-->    <html#{attrs} class=\"no-js\"> <!--<![endif]-->",
    capture_haml(&blk).strip,
    "</html>"
  ].join("\n")
end

call it like this in the layout:
!= conditional_html(:lang => I18n.locale) do