You have several options that are documented here on the nation:
- Dynamic Content+Segment by Country for that module where you say Segment By Country and then 4 URLs and 4 Content items in the Asset. (accurate)
- 4 emails as you said with 4 smart lists (accurate!)
- "Coupon Field Method" where you create a field like "Coupon" and upload the URL or portion of URL that will be different. Then export smart list, update the Coupon column by Country, re-upload just Coupon+Email Address (assumes no dupes). Then place token in the location of the URL instead. (less accurate)
You do have to take time to setup any of these methods. I personally think the amount of work is effectively the same and you'd only save time in the future if you continue to run similar campaigns.