$ sudo apt-get update
$ sudo apt-get install roundcube-plugins-extra 

roundcube-plugins-extra is installed in your system.

Make ensure the roundcube-plugins-extra package were installed using the commands given below,

$ sudo dpkg-query -l | grep roundcube-plugins-extra *

You will get with roundcube-plugins-extra package name, version, architecture and description in a table

roundcube-plugins-extra package basic information: