Gardin and English curtain come via German and French respectively from vernacular Italian and back to Late Latin cortina with the same meaing. But before that there is confusion: In classical Latin cortina means 'round vessel, cauldron', from Latin cohortem 'enclosure, courtyard'. Evidently, according to Online Etymology Dictionary , the sense ‘curtain’ came because of a loan translation from Greek aulaia ("curtain") because the Greek word was connected to aule ‘court’.
When I was a child we had the same arrangement at the kitchen windows: a lace gardinkappa on top and plain white curtains below. Nowadays it out of fashion.
(So now I had to look up gardinkappa in my English dictionary. It translates as 'pelmet' or '(curtain) valance'.