You can either download it from GitHub or get the class through Composer (which is recommended).
Add the package to your composer.json file
{
"require": {
"algo26-matthias/idna-convert": "3.*",
},
}
Run php composer.phar update
.
The project's repoistory is also hosted at GitHub.com. As such you can easily clone the repo like so:
git clone https://github.com/algo26-matthias/idna-convert.git
The official ZIP packages are discontinued. Stick to Composer or Github to acquire your copy, please.