Asumaru

“Multisite Language Switcher” is very attractive plugin. 
However, It may not be available for your site plan.
<ul>
<li>Site A (English) example-site.com/</li>
<li>Site A (Japanese) example-site.com/jp/</li>
<li>Site B (English) example-site.com/siteB/</li>
<li>Site B (Japanese) example-site.com/siteB-jp/</li>
<li>Site C (English) example-site.com/siteC/</li>
<li>Site C (Japanese) example-site.com/siteC-jp/</li>
</ul>
“Multisite Language Switcher” cannot tell the difference between site A, site B and site C. 
Therefore you cannot connect the language when there are site A, site B, site C.
“MSLS Grouping” adds “group_key” to settings of “Multisite Language Switcher”. 
For example, you set “group_key” with “SiteA” or “SiteB” or “SiteC”. 
You can limit a language site in a group by doing this plugin. 
You can display only the first site when there are multiple same language sites in a group.
And, it provide shortcode “SameLangSites” and widget “SameLangSites”. 
You can output the list of different groups of the same language. 
For example, “SameLangSites” of “site A (English)” lists ” site B (English)” and “site C (English)”.
<ul>
<li>Site A (English) => Site B (English), Site C (English)</li>
<li>Site B (Japanese) => Site A (Japanese), Site C (Japanese)</li>
</ul>
And, it provide “Language” column on the Table of Sites in network.
And, it provide “Language Flag” in Admin-Bar.

MSLS Grouping

You can multilingualize by "Multisite Language Switcher" with grouping the sites of the plural same languages.

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 if you look for an easy way to change the output of the Multisite Language Switcher as an HTML select with some JavaScript that forwards the visitor automatically after selecting an option then give MslsSelect a try.

MslsSelect

Transforms the output of the Multisite Language Switcher to an HTML select

MSLS Grouping vs MslsSelect