libidn11 software package provides GNU Libidn library, implementation of IETF IDN specifications, you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install libidn11
libidn11 is installed in your system.
Make ensure the libidn11 package were installed using the commands given below,
$ sudo dpkg-query -l | grep libidn11 *
You will get with libidn11 package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | Libraries |
| Package | libidn11 |
| Version | 1.32-3ubuntu1.1 [amd64, i386], |
| Description | GNU Libidn library, implementation of IETF IDN specifications |
| Sub Section | Libs |