I wanted to post a comment to the answer just above but I don't have enough reputation.

You need to install php-intl with MacPorts as said above, but you're having trouble because MacPorts doesn't install the extension in the right place.

Find out where it was installed (MacPorts documentation for php-intl depending on your version)

For me it's : /opt/local/lib/php82/extensions/no-debug-non-zts-20220829/intl.so

So I copied the intl.so file and pasted it here: /Applications/XAMPP/xamppfiles/lib/php/no-debug-non-zts-20220829

And that's it