woocommerce checkout conditional fields based on radio buttons choices

Solution:

I’ve managed to make it work. I’m posting here in case it could be useful to others

add_action( 'woocommerce_after_checkout_form', 'cbi_cf_conditionally_hide_show', 6);
function cbi_cf_conditionally_hide_show() {
    // if ( ICL_LANGUAGE_CODE !='it' ) return; // Only for Italy
    $required = esc_attr__( 'required', 'woocommerce' );
    ?>
    <script type="text/javascript">
        (function($){
            var required = '<abbr class="required" title="<?php echo $required; ?>">*</abbr>'; // Required html

            $('#billing_cf_in_field').hide();

            $('input[type=radio][name=billing_radiobox_cf]').change(function(){
                if (this.value === 'option2') {
                    $('#billing_cf_in_field').fadeIn("fast", function(){
                        $(this).addClass("validate-required");
                        $('#billing_cf_in_field > label').append(required);
                    });
                } else {
                    $('#billing_cf_in_field').fadeOut("fast", function(){
                        $(this).removeClass("validate-required");
                        $('#billing_cf_in_field > label > .required').remove();
                    });
                }
                $('#billing_cf_in_field').val('');
                $('#billing_cf_in_field').removeClass("woocommerce-validated");
                $('#billing_cf_in_field').removeClass("woocommerce-invalid woocommerce-invalid-required-field");
            });
        })(jQuery);
    </script>
    <?php
}

Unfortunately, validation is not completely working, since when sending the form, in case billing_cf_in_field is not filled, the field becomes correctly red but the error message does not mention billing_cf_in_field in the list of fields to be fullfilled. I’ll open another thread for this.