Have all "ipad mini 2"s a retina display? I want to buy a iPad mini 2 and I'm searching about it. Actually I'm confused. Somewhere people call it just "iPad mini 2" and somewhere else "iPad mini 2 with retina display" ..! 

Ok, all of them have retina display? Or there is some iPad mini 2 which don't have a retina display?
Yes, every model of the iPad mini 2 has a retina display. Those who call it the "iPad mini 2" are likely just using a shortened form of the name for convenience.

Source: apple.com