Just my 0.02$.
Did you login into dl.com?
What address do you have (country) in their files for your SM account?

When I had Korean address all the flights (including domestic US, or EU-US) were priced in Korean wons. Now with US address I have all flights (EU-US, Korea-US, even Russia-US) priced in US$.

Anyway, even when I had flight priced in Korean wons, on the last booking page before payment the system asked in which currency I would like to pay, wons or US$, and showed price in both currencies.