wcml_custom_prices_fields_labels

/*
 * Add this code to the functions.php file of your theme.
 */
add_filter( 'wcml_custom_prices_fields',  'add_custom_price_fields', 10, 2 );
function add_custom_price_fields( $fields, $product_id ) {
    
    // Add a new custom price field 
    $fields[] = '_sign_up_fee'; 

    return $fields;

}


add_filter( 'wcml_custom_prices_fields_labels', 'set_labels_for_price_fields', 10, 2 );
function set_labels_for_price_fields( $labels, $product_id ){

    // Edit the label of a custom price field
    $labels[ '_sign_up_fee' ] = __( 'Sign-up Fee', 'woocommerce-multilingual' ); 

    return $labels;

}