This translation does not confirm with our rules. Please rewrite as:

     html = vm.ready? ? { :confirm =>_("Are you sure you want to power %{act} %{vm}?") % {:act => action_string(vm).downcase.strip, :vm => @vm}, :class => "btn btn-danger" } :

The same bellow.

More info here: http://projects.theforeman.org/projects/foreman/wiki/Translating