I would prioritize my future career over “something I have always wanted to do”…as your career starts at a certain point in time and you can continue to learn spanish over a lifetime.
I don’t even think the OP is prioritizing career over something they have always wanted to do. They are getting part of that – 1 year vs 1 semester isn’t actually that big a difference.
I would study abroad in Spain for a year.
You have your whole life to work in DC. You can move to DC after you graduate college and work or intern there. But after you finish college, your opportunities to live abroad for long periods of time diminish unless you have significant language fluency and land a job that can pay for it.
Sure, you can learn Spanish over a lifetime - but taking night classes when you’re working full-time as an adult is totally different from living and learning in Spain on the ground for a full year. And you’re right by saying your fluency can jump so much when you do a year.
I’m not saying that your future career isn’t important, but you have so much life ahead of you to prioritize that career. Really, after you graduate from college, you’re going to be working for the next 40-50 years of your life. “Something that I have always wanted to do” is really important, too.
ONE of my best memories from college was the semester I studied abroad, and one of my regrets is that I didn’t study abroad for a full academic year.