Woocommerce add a custom field to checkout form (ex: tax number 統一編號 in Chinese)

functions.php

/**
 * Add new field to Checkout
*/

// Hook in
add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields_add_tongbian' );

// Our hooked in function - $fields is passed via the filter!
function custom_override_checkout_fields_add_tongbian( $fields ) {
     $fields['billing']['billing_tongbian'] = array(
        'label'     => __('統一編號', 'woocommerce'),
    'placeholder'   => __('輸入統一編號', 'placeholder', 'woocommerce'),
    'required'  => false,
    'class'     => array('form-row-wide'),
    'clear'     => true
     );

     return $fields;
}

//Edit on Dashboard edit order page

add_action( 'woocommerce_admin_order_data_after_shipping_address', 'my_custom_checkout_field_display_admin_order_meta', 10, 1 );

function my_custom_checkout_field_display_admin_order_meta($order){
    echo '<p><strong>'.__('統一編號').':</strong> ' . get_post_meta( $order->id, '_billing_tongbian', true ) . '</p>';
}