Áo lạnh = Shirt cold. It's so funny to wear a cold shirt when you need warm clothes!
actually, from how I perceive it, any upper wear which has the purpose to keep one warm is considered áo lạnh.
as for áo khoác, any types of coats that are open down the front, closing by means of buttons, zippers, hook-and-loop fasteners, toggles, a belt, or a combination of some of these, would be considered as is (coat, cope, jacket, mantle, overcoat, pall, mantilla, dressing gown, outerwear, paletot, etc.)
In English one would always say coat and sweater, not sweater and coat. I wonder if there's some kind of rule for order in Vietnamese?
How come my dictionary says ao len dai for sweater and ao vet for jumper?
len is a loanword from the French laine which means wool.
vét is also a loanword from the French veste which in VNmese refers to the suit jacket more than any other jackets.