[hackissimo123]

To add to this, "endangered" languages aren't necessarily those with few speakers, and languages with few speakers aren't necessarily endangered. What matters is how many children are being raised to speak the language; some languages are rare but are in no danger of dying out (at least not within the next generation) while others are more common but the speakers are disproportionately old and few children are learning it.

I don't know much about Yiddish but I believe it's in the former category. Yiddish was by far the most common language among Jews who were murdered in the Holocaust; there are still fewer than 10% as many Yiddish speakers in the world today as there were in 1930. But according to Wikipedia "the number of Yiddish-speakers is increasing in Hasidic communities."

[amitport]

Yiddish really isn't going anywhere and there are still plenty of children raised to speak it. So it is (perhaps surprisingly) in the latter category (only among (ultra?)orthodox Jews, but they're not endangered).