As someone who doesn't do software development as part of routine day-to-day work but has played with both, I'd describe Julia as "Fortran for Python developers", while Nim feels like "C for Python developers".
My interest in scientific applications pushes me towards Julia, but the user experience has so far been strictly worse than than Python, so I just don't bother with it as much as I might like to.
On the other hand, I am drawn to experiment with Nim (and to some extent Rust as well) because they feel better constructed, having more professional feeling tools and approaches to packaging. The downside is that their core strengths are in use-cases which aren't so aligned with my interests.
The strength of the Python packaging ecosystem makes me doubtful of the impact Julia can have. Meanwhile for Nim, it feels to me like awareness and adoption suffer a fair bit from competing with Rust for mindshare.
You can pick both, they are very different. Julia is a dynamic language looking for a compromise between interactivity and performance (from it's origin on R/Matlab), while Nim is one of the new batch of static languages that looks for the perfect balance between of easy of development and safety/speed.
For example, if you want to do something more exploratory (like some research or data analysis) that can still easily scale up to HPC you can use Julia, if you want to create something reliable with small binaries and no start-up issues or use in more resource constrained environments you can use Nim.
Not that @ddragon exactly said you could not, but you can also use Nim for data science, such as https://mratsim.github.io/Arraymancer/ or https://github.com/Vindaar/nimhdf5 or many others and there is a REPL INim mentioned in another comment here. If you want everything "done for you already", Julia has more libraries and it is (for better or worse) more fundamentally dynamic.
My interest in scientific applications pushes me towards Julia, but the user experience has so far been strictly worse than than Python, so I just don't bother with it as much as I might like to.
On the other hand, I am drawn to experiment with Nim (and to some extent Rust as well) because they feel better constructed, having more professional feeling tools and approaches to packaging. The downside is that their core strengths are in use-cases which aren't so aligned with my interests.
The strength of the Python packaging ecosystem makes me doubtful of the impact Julia can have. Meanwhile for Nim, it feels to me like awareness and adoption suffer a fair bit from competing with Rust for mindshare.