Wikipedia has a "List of Languages by time of extinction".
I think, for the most part, the term "dead language" evokes Latin. But Latin, while not the official language of a country, say, is still used. Ish. Students still learn it. You can still hear a Mass in it. I think perhaps exorcisms tend to be performed in it. I mean, I'd want my exorcism to be in Latin, should I ever occasion to require one. Take this as official record of my wishes.
Oh, Wikipedia educates me that "dead languages" differ from "extinct languages", wherein an extinct language no longer has speakers and/or is no longer in current use. A dead language is known in written form, but may no longer be used daily. Completely different, natch.
(I am not a linguist. Can you tell? Though a college class I enjoyed very much was a 400 level philosophy one called "Language, Meaning, and Truth" wherein I learned such tidbits as the more you try to explain something, the less clear it becomes, and Wittgenstein hates you [these are two separate thoughts]).
But the recent extinction of language, or the extinction of languages at all, is kind of eerie. It bugs me, to say the least. It's like in 7th grade, when we learned about the Rosetta stone, and I was all "Wait, wait, there are still Egyptians in Egypt. There have been all along. They can't read Egyptian? How does that happen?" (The answer to the Egypt question is, I think, that those Latin-speaking conquerors really did a number on them.) But I mean, the Manx-Celtic, according to that list, went out in 1974. That's recent. There are more recent examples, but I picked that one essentially at random. Though apparently it's making a resurgence; that's one thing to be said about educational systems, they'll frequently take your homeland's language and cram it down your throat. I remember Frank McCourt mentioning this in Angela's Ashes.
But some of the more recent ones, it's because the last native speaker died. Like the language of Livonian, which died in 2013. Can you imagine being the last one in the world who speaks your language? The implications are boggling, to be sure. Evidently, there's an Endangered Languages program, for just this type of issue, which I think is neat. Intellectual conservatorship (conservation? Conservating?) is something I can get behind.