In this post, I will show you how we can add missing PHP 7.2 missing extension using Ondrej PPA in Linux server.
apt update apt autoremove
Once you have fixed that issue, you can try executing following commands if you have not added Ondrej PPA:
add-apt-repository -y ppa:ondrej/php apt install php7.2-intl
Now you can restart your server.
sudo systemctl reload php7.2-fpm.service