WordPress at a glance
action is not described

wp_validate_site_deletion action-hook . WP 5.1.0

Fires before a site should be deleted from the database.

Plugins should amend the $errors object via its WP_Error::add() method. If any errors are present, the site will not be deleted.

Usage

add_action( 'wp_validate_site_deletion', 'action_function_name_527', 10, 2 );
function action_function_name_527( $errors, $old_site ){
	// action...
}
$errors(WP_Error)
Error object to add validation errors to.
$old_site(WP_Site)
The site object to be deleted.

Where the hook is called

wp_delete_site()
wp_validate_site_deletion
wp-includes/ms-site.php 220
do_action( 'wp_validate_site_deletion', $errors, $old_site );

Where the hook is used (in WP core)

Does not used.