We all know the reason for 4 cups that Rashi/Rasbam quote from the Yerushalmi in the beginning of Arvei Pesachim. The explanation is the cups correspond to the 4 leshonos of geulah.
However the Yerushalmi lists a number of other explanations. Rebbi Yehoshua ben Levi explains that the 4 cups are connected to the 4 times the word 'Kos' is used in the dream of the 'sar hamashkin' as he tells the dream to Yosef*.
I don’t think the message that Rebbi Yehoshua ben Levi is trying to convey is so obvious. Clearly there can be numerous explanations - but does anybody have an explanation that connects the 4 kosos in his dream and the 4 kosos on the leil ha’seder?

* Leaving alone the fact that ‘Kos’ is mentioned 5 times (see Torah Temmimah on that point.)

Sorry to bother you, but I looked up "leshonos" and "geulah" in the bigger Hebrew glossare that was recommended, but only "geulah" was there. What does "leshonos" mean?

In the "geulah" explanation, it mentioned Jews coming together "from the 4 corners of the world." Could the 4 stand for the 4 corners?

Actually, it bothers me to read about "4 corners" in something written by Hashem (or wasn't it?). Surely He knew that the world is not square and flat. Or was He just speaking picturesquely?

And since I'm learning in various posts about the symbolism of matzoh and wine, is there a web source where I can go to find out the meanings of the other foods on the Passover table? I have heard mostly the same explanations year after year, and apparently there are explanations I have never heard of! (I also realize that more than one explanation may be relevant.) Thanks.

The conection could be that that dream propelled Yosef into office, thus bringing Klal Yisrael to Egypt.

(the "4 corners" could be no more than the "edges" of the 4 directions E,W,S,N)