How does Observable Plot work here? Do you translate the code to JavaScript?

The scripton Python library internally transforms many common Python data formats (regular arrays and dicts, numpy arrays, data frames, ...) to an intermediate format. These are transferred to the IDE when you call the plotting functions, and then auto-translated into the JS equivalent.

Your Python plotting code ends up looking like this: https://docs.scripton.dev/api/plot/orion/overview