We detached this subthread from https://news.ycombinator.com/item?id=15197488 and marked it off-topic.
Yet, there are languages that are in decline, because the population has dispersed or has been assimilated into other cultures. Some have less than 100 speakers, some are extinct. These languages are not just only tools for communication. They have evolved along with their speakers and thus reflect their culture and history.
Just as examining the DNA of a species can shed light on where it originated from, its habitat, challenges it evolved against and so on, so can the morphological analysis of the language text and word etymologies, enable one to map out invasions and associations with different cultures, periods of famine and plenty, the important aspects of the culture etc. For example, Eskimos have numerous words for snow because their lives depend on nowing the nuances of different types of snow and adapting to it. The movement of people in Central Asia, thousands of years ago, can be deduced from the tree of languages that have branched out from the original settlers. I will try to add references soon.
Languages are a part of history, a part of human culture, a part of us. Death of a language is death of a civilization, a way of life (though the people themselves may live on). Preserving the vestiges of a dying language is a noble act in service of the human civilization, future and past.
[1] https://en.m.wikipedia.org/wiki/Telugu_language
Edit:fixed typo
What is the tangible benefit (in excess of the time investment) of dead languages?
And this may be a little naive but, it is nice to preserve human history in its original format, but how can that help the average person?
[0]: https://mobile.nytimes.com/2014/12/07/opinion/sunday/why-sav...
When I speak other languages I tend to be more serious. Perhaps this is because I was very serious when I was studying them? (Perhaps causation goes the other way?)
The whole point of wikipedia is to preserve everything. Especially since people who speak the language are clearly underserved online.
I don't see much value in maintaining the regular, daily use of any particular language, but I see tremendous value in preserving the written works (and nowadays spoken audio) of every language. It provides informative data to anyone seeking to understand language, history, and culture, today and in the future.
For the same reason, I support preserving all source code, even from discontinued or unfinished or shitty software. I have no idea what types of analysis might be possible in 500 years, but I don't want to deny them the opportunity to try it.
You often hear the concern that regional languages could disappear because most parents would prefer that their kid studied in an English medium school.