It is common to hear yeshiva bochurim criticized for speaking Yinglish, a form of Yiddish influenced and inflected English (If you don't know what I mean listen to number 7, here ). I am somewat conversant with the dialect but still find it difficult to express myself clearly and precisely in it (and in my experience so do others). It is interesting to realize that even in Talmudic times, the scholars spoke a dialect that was neither spoken by the population at large and not by the Jews.
We have, for example, several accounts of amoraim not understanding common speech. Rovo seems to be at the center of several such reports. He did not know what "kiddusha rabba" means in Pesachim 106a, or what "terima" is (Brochos 38a).
"A certain rabbi asked Rovo, "what blessing does one make on terima"? He did not know. Ravina was sitting before Rovo. He asked: "Do you mean if it is made of seasame or of "grape mush"... So Rovo reminded hmself (of what this meant". He said: You mean chashilta...."
This is what Maharsho writes on Rosh Hashana 26a
" We find the rabbis at times used neither the language of verses nor the language in which people spoke. Sometimes they did not even know the language of the rabbis, as it says in chapter "asara yuchasin". R. Nachman said to R. Yehuda, "I made pursa d'gundara". He told him, "Why would it bad to say "maaka (fence)" as the verse calls it, or "mechitsa" as the language of the rabbis... (and other examples)"
R. Nachman was, of course, an aristocrat (Seder ha-Dorot, pp. 283) who was close to roylaty and he was the exilarch's son-in-law, and yet he apparently spoke yeshivish. only. He was fond of collecting folk saying(see Yoma 28b-29a), and used popular expressions in his speech (Chullin 12a, 172a; Ta'anit 24a).
The House of Rebbi, on the other hand, was keen on languages. Rambam writes in the Introduction to the Mishna that even the maids in his houshold spoke Biblical Hebrew well.
The source for this is here (Rosh Hashana 26a)
The Rabbis did not know what was meant by serugin, until one day they heard the maidservant of Rabbis household, on seeing the Rabbis enter at intervals, say to them, How long are you going to come in by serugin?
The Rabbis did not know what was meant by halugelugoth, til one day they heard the handmaid of the household of Rabbi, on seeing a man peeling portulaks, say to him, How long will you be peeling your portulaks? (halugelugoth).
The Rabbis did not know what was meant by, salseleah (and it shall exalt). One day they heard the handmaid of the house of Rabbi say to a man who was curling his hair, How long will you be mesalsel with your hair?... [Then comes a similar example which does not involve Rabbi Judah’s maidservant. I
The Rabbis did not know what was meant by we-tetethia bematate (of destruction), til one day they heard the handmaid of the household of Rabbi say to her companion, Take the tatitha (broom) and tati (sweep) the house.
The Rabbis did not know what was meant by Cast upon the Lord thy yehab and he shall sustain thee. Said Rabbah b. Bar Hanah: One day I was travelling with an Arab and was carrying a load, and he said to me, Lift up your yehab and put it on [one of] the camels.
The more things change, the more they remain the same.