Populate WPLANG site option when setting up a network. Props SergeyBiryukov. fixes #21726

git-svn-id: https://develop.svn.wordpress.org/trunk@22257 602fd350-edb4-49c9-b593-d223f7449a82

wp-admin/includes/schema.php

@@ -910,6 +910,7 @@ We hope you enjoy your new site. Thanks!
 		'ms_files_rewriting' => is_multisite() ? get_site_option( 'ms_files_rewriting' ) : '0',
 		'initial_db_version' => get_option( 'initial_db_version' ),
 		'active_sitewide_plugins' => array(),
+		'WPLANG' => get_locale(),
 	);
 	if ( ! $subdomain_install )
 		$sitemeta['illegal_names'][] = 'blog';