Yossi –
This one, I gotta do in English.
The only way to really learn the lingo is to hang out with Yiddish speakers. And in today’s market, that means Chassidim. The rest of us speak it, but not enough for you to really pick up all the nuances.
Forget online, forget Rosseta Stone. Wanna speak like a brotha’? Make yourself at home in the sheeble. Give it 6 months to a year, and you’re in.