You often hear the concern that regional languages could disappear because most parents would prefer that their kid studied in an English medium school.
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.