"Kona mi vil ha en nyere bil."

Translation: My wife wants a newer car.

[Webb.Paul]

La den yngre mannen kjøpe det til henne!

[YiRuiLim]

Jeg vil ha en nyere kone...

[BurekAuFromage]

Husker janteloven, kona!

[vtopphol]

*husk

[kelac68]

Si henne at hun ville se eldre ut i en nyere bil!

[Martin633120]

When she wanted a younger husband, Duo suggested "Kona mi ønsker seg en yngre mann". On that premise I used "ønsker seg en ny bil" here, but Duo rejects it. Why?

[vtopphol]

I would say you're translation is fine. If you want to be precise, "ønsker seg" is more akin to "wishes for" while "vil ha" is closer to "wants". But the basic meaning, in both English and Norwegian, of the two phrases, is the same.