package management - Installing library with foreign architecture

I have been trying to install libc6-i386 on ubuntu 16.04 using:
sudo apt-get install libc6-i386 and the command line gave the following error: sudo apt-get install libx11-6:i386.

It seems that it cannot detect packages from other arch type.

I already did the following:

sudo dpkg --add-architecture i386
sudo apt-get update
sudo apt-get install libx11-6:i386

Checking from the Synaptic package manager, it does not display any packages/library from i386 architecture. How to install library from other architecture?

The system I'm running in is NVIDIA jetson tx1 with L4T R28.2. It's based on ARM64 and I need to run Arduino IDE which is based on ARM32.

---

source.list:

deb http://ports.ubuntu.com/ubuntu-ports/ xenial main restricted universe multiverse
deb-src {---} xenial main restricted universe multiverse


deb {---} xenial-updates main restricted universe multiverse
deb-src {---} xenial-updates main restricted universe multiverse

deb {---} xenial universe
deb-src {---} xenial universe
deb {---} xenial-updates universe
deb-src {---} xenial-updates universe

deb {---} xenial-backports main restricted
deb-src {---} xenial-backports main restricted


deb {---} xenial-security main restricted universe multiverse
deb-src {---} xenial-security main restricted universe multiverse

Regards,
Kezia