Rick Curran

WordPress 5.9 added a new language selector to allow users to switch languages from a dropdown on the login screen if more than one language is enabled on your WordPress installation. This plugin provides a quick and easy way to prevent this language selector from appearing.
It is a very simple plugin which is provided for ease of use: you need only to install and activate the plugin and it will prevent the language dropdown from appearing on the login screen of your site.
Alternatively, you can also achieve the same effect by adding the following line of code to the <code>functions.php</code> file in your theme:
<pre><code>add_filter( 'login_display_language_dropdown', '__return_false' );
</code></pre>

Disable Login Language Selector

Remove the language selector from the login screen if you have more than one language enabled in WordPress 5.9 and later.

Rick Radko

A plugin that adds language indicators, either a flag, locale or language, beside the site title of sites to help identify similarly 
named sites in multilingual multisites. This is most helpful in sites with admin language selectors, where the admin language does not 
reflect the site language.
There is a French translation of this plugin included. The French translation was created mostly to test the localization of the plugin. 
It’s a “machine” translation, and as a result, not very good. If you can improve it, or provide translations for other languages, please let me know.

R3DF Multisite Language Indicator

Adds language indicators (flag, locale or language) beside the site title of sites to help identify similarly named sites in multilingual multisites.

Disable Login Language Selector vs R3DF Multisite Language Indicator