Cahanging the Interface Language

I have recently moved over to using www.ads-software.com instead of wordpress.com to take advantage of plugins etc. However I want the interface to be in Italian since I have a couple of Italian customers. On wordpress.com this is an option in settings but on www.ads-software.com this option has gone.

Can anyone tell me if it is possible to change the interface language and if so how?

I have even downloaded and installed what I thought was an Italian version of wordpress from https://www.wordpress-it.it but still the interface remains in English.