A little history of Aramaic and the Jews:
There are sources that indicate that before mattan torah, the Jews spoke Aramaic. regardless, after mattan torah they spoke Hebrew exclusively. Due to the spread of the Assyrian and Babylonian empires, Aramaic became “the” common tongue of the Middle East. When the Jews were exiled, they switched to Aramaic. When they came back to Eretz Yisroel, they kept Aramaic. Later, Alexander the Great conquered the Middle East, and Greek became the lingua franca (literally “French Language”, ie. the common tongue). The Jews kept speaking Aramaic. the rabbis spoke Mishnaic Hebrew. The Hellenists spoke Greek. We find Greek names later appearing among the Jews, like Hyrcanus, Theodotus, Todros, Sumchus, etc. The anti-semitic “Passion” movie was done in Aramaic because that was Yoshke’s native language, the language of the am. This is the background for Rebbe’s statement about Aramaic- either Loshon Hakodesh or greek. Aramaic was passe’ as a common tongue, and it wasn’t loshon hakodesh. The same can be said for Yiddish. The Torah is holy. Lashon Hakodesh (Both lashon hatorah and Loshon chachamim, aka Mishnaic Hebrew)is holy. Yiddish is NOT holy. You don’t say birchas haTorah before reading the anti-religious works of Shalom Aleichem or an old copy of the socialist Yiddish Forward. In fact, you don’t read them at all, even if they’re written in Yiddish.
That said, some of the best shiurim in the yeshivos in eretz Yisroel are given in Yiddish. It’s good to learn yiddish as an eitza tovah if you want to attend the top Yeshivas. Otherwise, I’ll listen to the words of my Rosh Hayeshiva ZT”L, a native Yiddish speaker- Yiddish has NO kedusha.
There is a midrash that says Hebrew is a lashon hakodesh because there are no not-nice words in it. The same can’t be said for Yiddish.
One of the biggest shandas by Rav Gifter’s Levayah in New York was that only one speaker spoke in English.