Translation:The ladies wear the modern dresses.
"Modern dresses" sounds a bit odd in American English. Appliances are modern. Clothes are not usually described as modern (except on Duolingo). So if German uses "moderne" to describe "Kleider," a better translation in English would probably be stylish, the latest, or fashionable.
Note: Duolingo does accept these better alternatives.
modern  mo•dern
1 adj modern no adv
(=zeitgemäß) [Maschine, Vorrichtung auch] up-to-date no adv
modern sein [Kleidung, Möbel] to be fashionable
modern werden to come into fashion, to become fashionable
der moderne Mensch modern man
---- I've got that definition too