My suggestion would be to experiment with languages until you find one that you like more than the others and replicate the functionality of someone else’s software. Free yourself of the need to come up with a good idea.
If you choose a language that’s not widely used or no one is hiring for, don’t worry about it. You’ll find that the concepts you learn in any language are portable to all languages. Once you learn those, it will be easy to pick up new languages when you need to.
Bonus advice: when you find a language you’re good at, stick with it and get really good at it.