Against speaking, that is. You may study Yiddish.
Nay, you should study Yiddish because it contains heilige (holy) Halacha and Masores. Agreed. Yes, the Shach did speak Yiddish (although many greats preferred Hebrew, as, to the best of my recollection, ignored by Vayo’el Moshe‘s section against Hebrew).
Another plus is, then you can absorb certain Shi’urim at gutte (good) Yeshivos.
Also, I keep davening (praying) minelayers mine through the whole Soloveitchik/Teitelbaum oeuvre (as opposed to just VM/Rabbenu Chaim Halevi), so being able to translate the Yiddish for those specialists would be important.
But don’t employ the ‘shprach fun Yiddish’ (Yiddish language) on purpose (unless it’s the best way available in your situation to stay away from modern, evil culture). Of course, plenty of the interesanteh vocabulary is just Hebrew or English or Arabic or…, as the saying goes of the man who spoke seven languages, all of them in Yiddish.
(And I don’t even wish to repeat the valid point copied here.)
Then why not speak Yiddish?
My strong conviction is: Spoken Yiddish has all the bitter, kvetching lack of Emunah of krechtzing (moaning) Jews for a millennium in Galus, and the “richer” the Yiddish, the more wretched the Yiddishkeit within, generally. The full implications of many of its expressions are wrong as seen by optimistic, Emunah eyes.
The language appears shlepping on its way out, anyway. Yiddish is promoted by the same sorts of nostalgic people who reject all other modern, God-given blessings.
Here’s an ad hominem commercial break:
It’s promoted in an idiotic fashion, too. I know of several Chadarim (day schools) located in Chutz La’aretz who insist on translating Chumash into Yiddish for their students who don’t understand either Hebrew or Yiddish. I try not to think about this dereliction of duty because it makes me ponder what Halacha can be learned from the story with Yo’av in Bava Basra 21a-21b (or worse).
End of the commercial break.
I am loath to try and prove this. My inner voice snipes “you can’t prove it” at every example I think of. Some will agree with this point on Emunah, and others won’t, no matter what I say. So I leave this at “So say I”. Absorb some good books on Emuna, and tell me if it honestly fits into Yiddish. I should think not. Tatteh zisse, Bashefer, Aibeshter, etc. is “Batel Berov”.
Not up to your usual standards, huh…?
I never said this was going to be the definitive, well-argued “case” against Yiddish!
Of course, I mean substituting Hebrew in its stead…