Let's start by noting that Norwegian continues to charge anywhere from 10-30% more (amount of rip-off varies according to the price, the city pair, and current foreign exchange rates) when paying in USD rather than NOK for its long-haul US routes (as well as its intra-European routes, although the difference seems to be lower for those). In select cases, SEK or DKK is the cheapest currency to pay in; this varies by city pair and direction (US to Europe vs. Europe to US).

Take for example their flagship route JFK-OSL. The lowest-priced flights in August currently cost $411.30 USD one way. Switch the country (language) in the top right to "Norge (Norsk)", and you'll see that the same flights are available for just 2,600 NOK, or about $315 USD at today's exchange rate. Paying in USD is $97, or 31%, more than in NOK; a very significant amount. As far as I can see on their website, there is no mention of DCC (dynamic currency conversion), no mention of a hidden "currency conversion fee" such as Airbnb's (theirs is 3% and can be defeated by lying about your billing country), or any way to opt out of their terrible USD exchange rates.

Unless, of course, you pay in NOK, which used to be as simple as changing the currency while on the US site. You used to be able to pay in any currency you liked using any country/language. Some time in the past couple months, Norwegian decided they didn't want people evading their currency trap, so they're now forcing all bookings made on norwegian.com/us to be paid in USD. This also means if you do want to pay in NOK to save your 30%, you have to switch the country to Norway to do so. But then you're subject to Norwegian's credit card surcharge, 1.99% of the total purchase price, from which bookings made via norwegian.com/us are exempt. It's pretty financially viable to exempt US customers from the dreaded credit card surcharge when they're unknowingly paying 30% more, don't you think? Note also the discrepancies between the USD and NOK prices for their flat-rate fees, some in excess of 30%, as well as their surcharge for booking connecting flights (it's always cheaper to buy two one ways).

I was under the impression that airlines filed their fares in NUCs ("neutral unit of construction"), and then current exchange rates between NUC and USD, NOK, EUR, etc were dynamically computed on some regular basis and displayed on booking sites. Norwegian seems to be doing things their own way. Does anyone with more knowledge of currency conversion for airfare have an insight into what's going on here?

One method to circumvent this robbery is (potentially; I haven't tried it) to buy a gift card in the amount of the flight you wish to purchase (something you can of course only do from their Norwegian language site), wait the egregious 72 hour period before you can actually use it, hope the fare doesn't increase, and then pay with CashPoints redeemed from the gift card instead of charging your card and paying their obnoxious credit card fee. Any other ideas?