wpmu_create_blog

/**
 * Create a site.
 *
 * This function runs when a user self-registers a new site as well
 * as when a Super Admin creates a new site. Hook to {@see 'wpmu_new_blog'}
 * for events that should affect all new sites.
 *
 * On subdirectory installations, $domain is the same as the main site's
 * domain, and the path is the subdirectory name (eg 'example.com'
 * and '/blog1/'). On subdomain installations, $domain is the new subdomain +
 * root domain (eg 'blog1.example.com'), and $path is '/'.
 *
 * @since MU (3.0.0)
 *
 * @param string $domain     The new site's domain.
 * @param string $path       The new site's path.
 * @param string $title      The new site's title.
 * @param int    $user_id    The user ID of the new site's admin.
 * @param array  $options    Optional. Array of key=>value pairs used to set initial site options.
 *                           If valid status keys are included ('public', 'archived', 'mature',
 *                           'spam', 'deleted', or 'lang_id') the given site status(es) will be
 *                           updated. Otherwise, keys and values will be used to set options for
 *                           the new site. Default empty array.
 * @param int    $network_id Optional. Network ID. Only relevant on multi-network installations.
 * @return int|WP_Error Returns WP_Error object on failure, the new site ID on success.
 */
function wpmu_create_blog( $domain, $path, $title, $user_id, $options = array(), $network_id = 1 ) {
	$defaults = array(
		'public' => 0,
	);
	$options  = wp_parse_args( $options, $defaults );

	$title   = strip_tags( $title );
	$user_id = (int) $user_id;

	// Check if the domain has been used already. We should return an error message.
	if ( domain_exists( $domain, $path, $network_id ) ) {
		return new WP_Error( 'blog_taken', __( 'Sorry, that site already exists!' ) );
	}

	if ( ! wp_installing() ) {
		wp_installing( true );
	}

	$allowed_data_fields = array( 'public', 'archived', 'mature', 'spam', 'deleted', 'lang_id' );