代码进入function.php 活动子主题（或活动主题）的文件。它可以工作。

add_filter( \'woocommerce_billing_fields\', \'woo_filter_state_billing\', 10, 1 ); 
function woo_filter_state_billing( $address_fields ) { 
    $address_fields[\'billing_state\'][\'required\'] = true;
    return $address_fields; 
} 

add_filter( \'woocommerce_shipping_fields\', \'woo_filter_state_shipping\', 10, 1 );
function woo_filter_state_shipping( $address_fields ) { 
    $address_fields[\'shipping_state\'][\'required\'] = true; 
    return $address_fields; 
}