$ sudo apt-get update
$ sudo apt-get install php-wikidiff2 

php-wikidiff2 is installed in your system.

Make ensure the php-wikidiff2 package were installed using the commands given below,

$ sudo dpkg-query -l | grep php-wikidiff2 *

You will get with php-wikidiff2 package name, version, architecture and description in a table

php-wikidiff2 package basic information: