How do you decide on what languages and/or frameworks to use in personal projects?

My uni work is done for the summer on Friday and I want to start working on a couple of side projects.

I use c# at work, and this year I’ve been doing Java and next year I’ll be doing python with uni.

There’s a handful of languages I’d like to work with, but I know that I’ll get the best out of picking one language and digging into it, but I’m not sure how to pick the right one.