YakYak is a free and open source (unofficial) cross-platform desktop client for Googles Hangouts instant messaging app and it comes right out of the box with a plethora of customization options including native desktop notifications and language translation.
There are many unofficial desktop clients that work nicely on Linux distros and YakYak is no exception. It runs without the need for Chrome or Chromium to be installed and is a lot more memory and battery-friendly that a handful of its counterparts.
If you are searching for an efficient desktop client for Hangouts then your search has probably ended.
Versions YakYak for Linux
ver: 1.4.4 : Nov 10.2017
Screenshots YakYak for Linux