Multiple independent menus

If you need multiple independent menus, you can create (empty) dummy root pages and arrange all menu items below either of them, e.g.

menu1
   item1-1
   item1-2
   ...
menu2
   item2-1
   item2-2
   ...

Then to display a menu, use the following code (here for menu1):

<ul>
<?php
  $bc = return_i18n_breadcrumbs(return_page_slug());
  get_i18n_navigation($bc[0]['url']=='menu1'?return_page_slug():'menu1',1,99);
?>
</ul>

Unless you use reasonable names for the dummy pages, you should probably not use the %parent% page in the custom permalink structure.

(If all but one of the menus are rather static, you could also hardcode them into your template instead)