If you want to move to Scandinavia, you can probably do it without your SO needing to learn another language.
I did US-to-Sweden in 2008 and it's shockingly easy to get by with only English here. To the point that, if you want to practice Swedish with strangers and they get any hint that you're a native English speaker, they'll immediately take advantage of the chance to practice their English instead. It's one of the major reasons why my Swedish is still atrocious after nearly a decade here. (The other major reason being my own laziness.)