Sonos will work in South Korea, Spotify will not.

The Move just requires a USB-C connection.

The Ones and Fives have a 100-240V 50/60Hz internal power supply, with South Korea requiring 220V/60Hz.

The plug type is F so you may require plug adapters.

Spotify is not listed as a supported country in the Spotify and Sonos Support page.

Excellent, except for Spotify. Maybe I can get by with Amazon Music? Or is there an Korean app equivalent to Spotify that can used on the Sonos App? 

Amazon Music is available in less countries than Spotify.

After a quick google search, Spotify as a native service has launched in South Korea, which needs a Premium subscription. There would be no Spotify music service within the Sonos app and Spotify Connect may not work with Sonos, but with the Five’s Line-In capability, you would be able to directly play Spotify on your Sonos system using an aux cable.

Note that the streaming services (Spotify in this instance), need to give legal authorization for Sonos to ‘carry’ their content in each region. So, if Sonos doesn’t currently carry Spotify in South Korea, but Spotify does have their service on their own app available, now would be a good time to start lobbying Spotify to give Sonos access. Those legal agreements, at least when I’ve had to deal with them, take more time than expected. 

We are here in Korea finishing up our 10 days holiday trip. And haven’t had any issues with Spotify. And yes I do have premium service.