I usually pick a second language that I'm either curious about or want to improve with, not sure what that'll be this year. I'm starting on a temporary assignment where we'll be using a lot of JavaScript so there's a decent chance I'll use it as my second language. I usually get about half the problems done with the second language before writing two (or three last year) solutions a day becomes too much of a time sink.
For my second languages I generally try to avoid any external libraries and focus on the language standards. If I pull in anything it's regexp/parsing tools if the base language doesn't have it as part of its library. Last year I also took a heavy TDD approach on my second implementation to try out Hypothesis (property-based testing for Python, great tool). I usually do a TDD-lite approach for my first solution in Lisp.
I've used Ada (2020), Rust (2021), Python (2022), and C++ (2022).
Since last year the most interesting languages I've read are Inko[0] and Jai, but I don't know the latter is available/ready. Pony is another one that's had my interest and I hadn't tried yet.
This year will be my first live advent of code. I've been learning programming in general and Nim language for the past half a year. And only start feeling confident with it.
So, while learning it, I've got through most problems of 2021 and 2022 AOC with multiple days or week-long delays between.
I'm a bit nervous to be burnt out by making myself go through AOC daily. Because I know how hard for me to solve the problems past first 15.