Mr Goldberg, from Pinsk, coming to America, shared a table in the ship's dining room with a Frenchman.
Mr Goldberg could speak neither French nor English; the Frenchman could speak neither Russian nor Yiddish.
The first day out, the Frenchman approached the table, bowed and said, "Bon appétit!"
Goldberg, puzzled for a moment, bowed back and replied "Goldberg."
Every day, at every meal, the same routine occurred.
On the fifth day, another passenger took Goldberg aside. "Listen, the Frenchman isn't telling you his name. He's saying 'Good Appetite,' that's what 'Bon appétit!' means."
At the next meal, Mr Goldberg, beaming, bowed to the Frenchman and said, "Bon appétit!".
And the Frenchman, beaming, replied: "Goldberg!"
(for those who like a good wine - but don't exaggerate ...) 
(for those who wish to remain sober ...)
http://www.workjoke.com/linguists-jokes.html
N.B.
In Russian: Приятного аппетита! (priatnovo appetjita)
In Yiddish: Est gezunterhayt! (yiddish)
Funny, when I was learning English, they told me that they don't say "good appetite"; they would rather say: "enjoy your meal".
But in the U.K., since a certain time, they seem to have adopted - with the time: "bon appétit!"
(unless aristocrats remembered that for a long time, French was their diplomatic and "court" language, as the links between the great dynasties and clans had spread to many different countries in Europe and elsewhere, i.e. "noblesse oblige"!).
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