It's not just about the currency, but also the value of the price. To use an example I have on my table right now, German newspapers and magazines usually target Austria and Switzerland as secondary markets and have different prices for each of them. So an issue that's 3.95 € in Germany can be 4.30 € in Austria and 6.30 CHF in Switzerland. Even though Germans and Austrians use the same currency, they don't pay the same price.
Why conflate the choice of language with the choice of currency? If there's a need to differentiate by those countries, give them that choice. If not, don't.
Or you could display everything in Korean to those with a Korean IP even though in some cases it will happen to be an Austrian who'd be thankful to see a German flag (or any flag!) on the screen to help them change the language. Then they can worry about the currency.
