Ask people to think about Sweden and invariably they will say IKEA. The massive flat-pack corporation has world dominance when it comes to home furnishings. However, in Germany, Swedish curtains are not necessary an attractive option.
To be ‘hinter schwedischen Gardinen’ (behind Swedish curtains) in colloquial German means to be in prison.
Not entirely sure of the reason but one theory is as follows:
German bars used to be made from strong Swedish steel, as they were particularly strong and escape-proof. When the bars formed a grille, they became the kind of ‘curtain’ that you don’t want to be behind!
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Watching the Swedes 
I do not know how Germans, but Poles are Ikea’s generation, Ikea company rules in their homes as a sign of good taste and taste. A wound less and less, because fashionable blinds.
Best wishes
It’s nothing to do with Ikea! The slang existed long before the founding of Ikea in WW2, and was used early in the century, I believe you’ll find the term mentioned in that 1925 autobiographical manifesto written in prison by the Nazi Party leader.