Any language can scale. Pretty much most languages there can handle scale. It's usually bad algorithms or external services be it API & DB used poorly that impacts performance.

Facebook uses/used PHP, that scales too. If you make it stateless and use it only as a glue. Dropbox uses Python too. Eve Online used Stackless Python.

Of course Reddit/FB/EVE/Dropbox shards everything, there's no global state to manage via Python. The state lives in the data store layer.

And for that there are these monstrous/elegant things like Vitess, that YouTube used (uses?): https://vitess.io/docs/overview/architecture/ which is basically a sharding/routing layer on top of independent MySQL instances.

And because of Instagram: https://instagram-engineering.com/python-at-scale-strict-mod...