It's usually more indicative of a language that's found in existing codebases, but is no longer used to start new ones. If you join a team and someone in that team actually knows Perl, that's highly unusual these days.

It's the same kind of "dead" as Latin: lots of folks actively use it, but meeting someone that does is pretty dang unusual unless you work for the Catholic church, in which case "everyone still uses it, what's dead about it?"