FIX: WooCommerce doesn't support attribute taxonomy creation on non startup.

wc-fix-pa-creation.php

<?php
/**
 * @wordpress-plugin
 * Plugin Name:       FIX: WooCommerce doesn't support attribute taxonomy creation on non startup.
 * Depends:           WooCommerce
 * Plugin URI:        
 * Description:       
 * Version:           1.0.0
 * Author:            chrono-meter@gmx.net
 * Author URI:        mailto:chrono-meter@gmx.net
 * License:           GPL-2.0+
 * License URI:       http://www.gnu.org/licenses/gpl-2.0.txt
 *
 * @see WC_Product_Importer::get_attribute_taxonomy_id()
 * @see WC_Admin_Importers::post_importer_compatibility()
 * @see wc_create_attribute()
 * @see WC_Post_Types::register_taxonomies()
 * @see WC_Product_Attribute::get_terms()
 * @see taxonomy_exists()
 */

defined( 'ABSPATH' ) or exit;


add_action( 'woocommerce_attribute_added', function( $id, $data ) {
	global $wc_product_attributes;
	$permalinks = wc_get_permalink_structure();
	$tax = (object) $data;

	$name = wc_attribute_taxonomy_name( $tax->attribute_name );

	if ( !taxonomy_exists( $name ) && $name ) {
		$tax->attribute_public          = absint( isset( $tax->attribute_public ) ? $tax->attribute_public : 1 );
		$label                          = ! empty( $tax->attribute_label ) ? $tax->attribute_label : $tax->attribute_name;
		$wc_product_attributes[ $name ] = $tax;
		$taxonomy_data                  = array(
			'hierarchical'          => false,
			'update_count_callback' => '_update_post_term_count',
			'labels'                => array(
				/* translators: %s: attribute name */
				'name'              => sprintf( _x( 'Product %s', 'Product Attribute', 'woocommerce' ), $label ),
				'singular_name'     => $label,
				/* translators: %s: attribute name */
				'search_items'      => sprintf( __( 'Search %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'all_items'         => sprintf( __( 'All %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'parent_item'       => sprintf( __( 'Parent %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'parent_item_colon' => sprintf( __( 'Parent %s:', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'edit_item'         => sprintf( __( 'Edit %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'update_item'       => sprintf( __( 'Update %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'add_new_item'      => sprintf( __( 'Add new %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'new_item_name'     => sprintf( __( 'New %s', 'woocommerce' ), $label ),
				/* translators: %s: attribute name */
				'not_found'         => sprintf( __( 'No &quot;%s&quot; found', 'woocommerce' ), $label ),
			),
			'show_ui'               => true,
			'show_in_quick_edit'    => false,
			'show_in_menu'          => false,
			'meta_box_cb'           => false,
			'query_var'             => 1 === $tax->attribute_public,
			'rewrite'               => false,
			'sort'                  => false,
			'public'                => 1 === $tax->attribute_public,
			'show_in_nav_menus'     => 1 === $tax->attribute_public && apply_filters( 'woocommerce_attribute_show_in_nav_menus', false, $name ),
			'capabilities'          => array(
				'manage_terms' => 'manage_product_terms',
				'edit_terms'   => 'edit_product_terms',
				'delete_terms' => 'delete_product_terms',
				'assign_terms' => 'assign_product_terms',
			),
		);

		if ( 1 === $tax->attribute_public && sanitize_title( $tax->attribute_name ) ) {
			$taxonomy_data['rewrite'] = array(
				'slug'         => trailingslashit( $permalinks['attribute_rewrite_slug'] ) . sanitize_title( $tax->attribute_name ),
				'with_front'   => false,
				'hierarchical' => true,
			);
		}

		register_taxonomy( $name, apply_filters( "woocommerce_taxonomy_objects_{$name}", array( 'product' ) ), apply_filters( "woocommerce_taxonomy_args_{$name}", $taxonomy_data ) );
	}

}, 10, 2 );