Also, it's a weird wonderland in which you know exactly which parts need to be fast, reimplement those, and then never need to touch those bits again. In my ex

Also, it's a weird wonderland in which you know exactly which parts need to be fast, reimplement those, and then never need to touch those bits again. In my experience, that's not the case - you're going to want to tune and alter your algorithm, and if it's API needs to go through several languages, it's going to be a pain. Every time you decide you need a slightly different input format or data store or set of hyperparameters, you'll likely be changing many more files than you would in a one-language solution, and in a way that's hard to unit-test and hard to statically type. It's certainly doable, and definitely the right way to go if you want number crunching in a high-level language, but it's not a free lunch. It's certainly not a quick one-time conversion and then you can forget about it.