They do host their own private "cloud", mostly used for research and project development.

> English Wikipedia gets about 250M page views per day, which is only about 3,000 per second. If they used an efficient language instead of PHP, that's well within the capability of a single modern server!

Nitpicking, page views from outside users are not supposed to hit PHP at all - those requests should be served by their caching layer. But yes, you're correct that they're relying on quite a bit of legacy tech from their early days, not just PHP but MariaDB as well even though many enterprises would now rely on Postgres wrt. these use cases. I suppose that they could rewrite the stuff piecemeal, and recent developments in PHP itself would make it easier. (Some things have been rewritten already, notably the wikitext parser. That's clearly one thing where you would want to avoid breakage at all costs, but they did get it done.)