I'm confused on the current state of this. In up-to-date Hugo, how does one set a custom Title for the 404 page to override "404 Page not found" (e.g. for a non-English website)? This is not covered by the doc.

There is a dozen of threads about this on the support forum, mostly from 2017-2018, without a clear conclusion that does not involve ugly hacks.

#585 is the closest I've found to in-depth information on the topic, but it was closed by the author for some reason.