You're echoing all stuff in double quotes ", so as you doing for class as well, in actual, this is happening
echo "<div class="pagination"><span>Pagina ".$paged." di ".$pages."</span>"
so if you pay attention, what is happening here is: echo "stuff class = "class" other stuff here!"
so you're putting double quotes(DQ) " inside DQ.
to make this work, wither you'll have to escape them properly(by putting back slash \ in front of each inner DQ like this
echo "<div class=\"pagination\"><span>Pagina ".$paged." di ".$pages."</span>"
OR simply using single quote ' for class = 'pagination' instead of DQs
if(1 != $pages)
     {
         echo "<div class='pagination'><span>Pagina ".$paged." di ".$pages."</span>";
     }