Hello! Does anyone know of a good place to go to start learning endangered languages?
Do you mean languages in a path of extinction?Well, I really don't know. But a good initial point for your research would be
Bhutan did a couple of important things to secure its existence: it strictly limited (largely Nepali) immigration in the earlier part of the 20th century, and it joined the U.N. in 1971; I think its existence is reasonably secure for the time being. Sikkim did neither of these things, and was swallowed up and occupied; I wish there were half the resources there are for Dzongkha for Bhutia and Lepcha (the main languages of the real Sikkimese)—they are much more deserving and teetering on the brink of a death spiral into functional extinction.
Irish Gaelic and Welsh (both of which are offered from English speakers on Duolingo) are endangered languages, but you can see all language courses at here:
You can find full lists of endangered languages at here: