Translation:The queen is wearing a big green dress.
Not idiomatic in English - at all. People would assume you were using great to mean “very good”. It’s just not used for the small things in the world like garments. “Great big dress” would work but it lends an informality to it. Actually I think “big dress” may not be all that idiomatic in English either but at least its meaning is clear. Big dress sounds ... uncomplimentary. “Gown” would probably be used instead, or adjectives like “sweeping”.
Before I heard the word Drottningen appear in Duolingo, I learned by listening to fairy tales in swedish that Drottning/en means queen, I just wasn't sure about the en ending but learning swedish in duolingo has helped me quite a lot.
Konungen means The king or kungen means also The king. In German König means King and Königin means queen in German so we don't have another word for queen we just use the same for king and add a female suffix "in" behind the word König, so it's Königin.
That's why I like that swedish has its own word for Queen.