$ sudo apt-get update
$ sudo apt-get install myspell-en-za 

myspell-en-za is installed in your system.

Make ensure the myspell-en-za package were installed using the commands given below,

$ sudo dpkg-query -l | grep myspell-en-za *

You will get with myspell-en-za package name, version, architecture and description in a table

myspell-en-za package basic information: