rfair404

This plugin makes it possible to have a menu that is controlled by the primary site but used throughout all other sites in the network.
<ul>
<li>When a navigation menu position has no menu assigned, the “fallback” defaults to pages. This plugin over-rides that so that instead it uses the nav menu from the “main site” (site ID 1)</li>
</ul>

Network Menu Fallback

Gives multisite administrators the ability to create menus that can be used throughout a network.

Dennis Ploetner

Most people are likely to use some lines of PHP or the widget provided by the <a href="https://wordpress.org/plugins/multisite-language-switcher/" rel="ugc">Multisite Language Switcher</a> to integrate the links to the translations in their blogs.
But this can lead to fatal errors if you don’t know much about PHP, or maybe the dynamic sidebars are not the best place in your opinion. If you want to integrate the Multisite Language Switcher in one (or more) of your Navigation Menu(s) then you should give MslsMenu a try.

MslsMenu

Adds the output of the Multisite Language Switcher to one (or more) of your navigation menu(s)

Network Menu Fallback vs MslsMenu