I tend to solve a problem that I fully understand in order to get a feeling for the language and what it can do. For example try programming a version of tetris or blockout. You know what the result should look like and will be able to evaluate how the language behaves, what apis there are and how well it is documented.

You might want to experiment with different types of projects, for example a little webserver, webscraper, games or general tooling for whatever problems you encountered before (I tend to write desktop cleaning programs a lot).

Maybe you can find inspiration in this book:

https://pragprog.com/book/btlang/seven-languages-in-seven-we...