I want to buy an ipad mini with retina display from amazon italy and want to know if I can change the language settings for everything (apps etc) to English? Or do I need to buy one from the UK?
It doesn't matter where you buy your iPad, a brand new one allows you to choose your preferred language out of the box, when setting it up for the first time. So there's no difference if you buy it in Italy or UK or any other country, you can choose the language the iPad will display (and change it whenever you want, in settings).
About the apps, usually they will use (or show up) the language that you set up in your iPad (if it is supported by the app). What I mean is there apps that when made, they only supported a specific language (or a few of them). e.g You set your iPad in chinese, but you download an app that only supports english, well it will be displayed in english, but if it supports chinese, it will be displayed in chinese. I hope I made myself clear.