Of course, one would think that in this day and age, if we feel that we need another language besides Hebrew, we should pick one equaly common to all of Clal Yisrael.
However, it is all a moot point. You want to speak Yiddish? Go right ahead. You can communicate with those who also speak the language. Of course, that means that for most day-to-day activities, you will not be communicating, as you certainly will have some trouble conducting your business in Yiddish, if it outside of Brookly, Lakewood, Bnei Brak, or certain neighborhoods of Yerushalayim.