Update on the use of international credit cards in Danish supermarkets:
Mastercard and VISA can be used in Kvickly, Kvickly xtra, SuperBrugsen, Dagli'Brugsen, LokalBrugsen, Irma, Fakta, and SuperBest.
SuperBest also accepts Maestro, American Express, V PAY, JCB, and China UnionPay.
For the use of MasterCard, Maestro, Visa, Visa Electron, V PAY, JCB, and China UnionPay use this store locator: http://preview.tinyurl.com/cvuyfd (I've set it for consumer goods in Copenhagen)
But, in Netto, Lidl, and Rema1000 you still need a Dankort...