Thank you for your reply. Now I explain in a detailed way what I did:
1) My idea was to create a web site both in English and in Italian and in order to do this, according to the official documentation of ProcessWire, I installed all the modules that you can find under the voice "Language" (Language Support) : in the admin page, Modules -> Core;
2) I have created a menu by means of admin page: Setup -> Menu Builder and here I created a menu with title "Menu_X" and then I built the menu by adding the pages that I wanted.
3) In order to have this web site in Italian and in English, in order to have the possibility to switch from one language to the other one, I added in each page this piece of code taken from the official documentation of ProcessWire:
$menu = $modules->get("MarkupMenuBuilder"); //load the module
$options = array(
'wrapper_list_type' => 'ul',
'list_type' => 'li',
'menu_css_id' => '',
'menu_css_class' => 'nav navbar-nav',
'submenu_css_class' => 'hvr-bounce-to-bottom',
'current_class' => 'active',
'current_css_id' => '',
'divider' => '»',// e.g. Home >> About Us >> Leadership
//prepend home page at the as topmost item even if it isn't part of the breadcrumb
'prepend_home' => 0,//=> 0=no;1=yes
'default_title' => 0,//0=show saved titles;1=show actual/current titles
'include_children' => 4,//show 'natural' MB non-native descendant items as part of navigation
'b_max_level' => 1,//how deep to fetch 'include_children'
echo $menu->render('Menu_X', $options); //render the menu
This is a select that allows to switch from English to Italian and viceversa.
4) Now when I created the "Menu_X", there wasn't the possibility to specify the titles of the different menu items in both languages and also the different urls: in fact the menu works only in the default language (English); what it seems strange is that when I switch from English to Italian, this error appears: "Fatal error: Exception: No menu items found! Confirm that such a menu exists and that it has menu items."
In the worst case, what I expected is to have the same menu both in Italian and in English. I would like to have how to create a multilingual menu with the right urls by means of Menu Builder.
Thanks in advance.