I have successfully transformed thousands of urls with the idn_to_ascii
function. But some (in my list about it is about 1%) are not - they look like normal url (not malformed), but i got empty string.
Example:
www.salonmeier.de/salon-meier-friseursalon-in-reichertshofen/datenschutz-und-impressum
PHP version is 7.0.12.