hyphen-it software package provides Italian hyphenation patterns, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install hyphen-it
hyphen-it is installed in your system.
Make ensure the hyphen-it package were installed using the commands given below,
$ sudo dpkg-query -l | grep hyphen-it *
You will get with hyphen-it package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Text Processing |
| Package | hyphen-it |
| Version | 1:5.2.1-2 |
| Description | Italian hyphenation patterns |
| Sub Section | Text |