I found a souluton.
header.php :
replace:
echo '<h1 class="entry-title">';
the_title();
echo '</h1>';
with:
$current_page = max( 1, get_query_var('paged') );
$total_pages = $wp_query->max_num_pages;
echo '<h1 class="entry-title">';
echo 'Page '.$current_page.' of '.$total_pages;
echo '</h1>';
I’m not a PHP coder, so I don’t know whether it is optimal or not, but it is working.
EDIT:
OK it IS working, but it breaks titles inside posts.
Any ideas?