After much deliberation, I decided to pick up Swedish. Spanish and Italian were the two other options, and while I would have a much easier time learning one of them, I took the path with the highest return-on-investment.
As I previously wrote, Sweden is the only country I see myself settling in, so this is what decided me. I've taken Spanish lessons for 8 years as well as a year of Italian, but I'm far from good and I don't feel any compelling reason to improve.
I completed my first one week streak today on Duolingo, and I started asking for advice from friends living in Stockholm. 15 to 30 minutes a day of learning a new language is all I can afford for now.
Once I'm done with the program tree, I'll start looking for technical blogs to read and subtitled videos to watch. In parallel, I'm going to translate some of my content with the help of a dictionary.
Another learning project I'm considering would be to take my Cornell notes and put them on a website, as I did with my book summaries for Sipreads (now deceased). Teaching is the best learning, and it would be a great way to showcase my skills if I were to actually migrate to Sweden.
I find Swedish extremely close to English for now, but let's see what I think of it in two months.