I'm planning on doing Politics, Chinese, Philosophy and Ethics and Music. Quite varied lol
In terms of your fourth option, I'd say do what you enjoy the most and want to carry on into your job... But if that's totally unhelpful, I say Spanish. Reasons:
1. You already have three essay subjects. I'm thinking about the welfare of your hand here.
2. You already have two social sciences so politics might be overkill.
3. Everyone loves a linguist!
I'm not kidding though, if you enjoy languages just throw yourself into it. It will be hard but you'll come out the end with at least semi fluency in Spanish! (hopefully)