As you may know, there isn’t any official WhatsApp client for Ubuntu and Linux systems, but this does not mean that there are no alternatives.
While WhatsApp can be used on Ubuntu and deb-based systems via the Franz messaging app, there is also another alternative available.
WhatsDesk is a community-based WhatsApp client available as a snap package. The latest version available is WhatsDesk 0.2.15 (stable), which is published as an open-source application, under the MIT license.
Due to the fact that WhatsDesk is available via a snap package, installing the WhatsApp client on Ubuntu 18.10 Cosmic Cuttlefish, Ubuntu 18.04 Bionic Beaver, Ubuntu 16.04 Trusty Tahr, Linux Mint 19.x, Linux Mint 18.x, Elementary OS 0.5 Juno and other Ubuntu derivative systems is easy.
All you need to do is install the snapd package (in order to use snap) and to use snap to install whatsdesk. Like this:
$ sudo apt install snapd
$ sudo snap install whatsdesk
Optional, to remove whatsdesk, do:
$ sudo apt remove whatsdesk