The Rashbam has an original explanation. He spoke JUST FINE! No speech therapy for him. [A little less parnassa for frum girls...] He just didn't speak Egyptian. Since he had left Mitzrayim so many years before, by the time he returned and he was supposed to speak to Paroh, he already forgot his Egyptian.
Asked Rav Chaim Zeitchik - Couldn't a genius like Moshe learn the language in a short time. I [meaning me Elchanan...] heard that Rav Hutner used to speak to the janitor in Chaim Berlin in Italian, which he taught himself on the two week boat ride over to America. The boys asked the janitor if the Rosh Yeshiva really knows Italian well or just knows a few expressions. He replied "If I'da knowa Italian like hima, I'd be'a in the United'a Nations...." If Rav Hutner could learn Italian so well so fast - Moshe could learn Egyptian, so what was his problem?
In Israel there are certain expressions and idioms that are really not Hebrew proper. If you live here long enough - you learn them. Otherwise, you could have a doctorate in Hebrew and not understand them.
Examples given of this phenomena:
Achla - Derived from the Arabic word "ahala" – Means cool, fantastic.
Eser - Literally "ten" - Means awesome, great
Sababa - This is a popular one used by young and old alike - Means cool, great
Pitzootz - Literally "explosion" - Means cool, awesome
Chaval Al HaZman (also Chavlaz if you're really cool!) - Literally "a waste of time" - Means awesome, amazing.
Al-a-Kefak - Derived from Arabic - Means really, really cool!
Al HaPanim - Literally "on the face" - means awful, bad - e.g. -"the pizza at that restaurant was "al ha’panim"
Eize Basa - derived loosely from the Arabic "yom asal yom basal" meaning "a honey day, an onion day" in other words - "what a drag"Fashla - Means a "mess up" - e.g. "The plumber did a real fashla on the shower hose.
Combina - A combina is also a concept unique to Israel in many ways. Derived from the English word "combination" it is a little hard to explain. Let's say you go to a hotel and end up paying partially for the bill with vouchers that you got from a friend as well as somehow getting the best price because you have a friend who is a travel agent, that's a combina. Basically using the system to your advantage, a pastime that is very popular in Israel. [My son once explained a Tosfos like this "תוספות עשו פה קומבינה". His Rebbi thought that was funny....]
Pa’am shlishit glida - As Israel is a small country it is normal for acquaintances to bump into each other a lot, sometimes even numerous times in a day. If you happen to bump into somebody twice in one day by chance you would say to them "pa’am shilishit glida" - which means that if you bump into them a third time they have to buy you an ice cream. [Recently I said this to my wife and then asked her what on earth it means:-)]
Explained Rav Zeitchik: Moshe could have learned the language perfectly, but the street expressions, the slang, the idioms etc. were foreign to him and he didn't WANT to learn them. The nuances of a language bring along with them a culture, a philosophy. Moshe didn't want to have any part of that world. That is what he meant [according to the Rashbam] when he said that I am a כבד פה.
This explanation positively tickled me when I realize that we recently posted a very similar [or the same] idea, here.
Four interesting notes:
1] The Rogochover says [similar to the Rashbam] that he couldn't speak the language [sans the explanation of Rav Zeitchik]. He says that Moshe Rabbeinu was עצם התורה and thus could only speak Lashon Hakodesh. It wasn't a chisaron, a flaw, but a myla, an indication of his exalted status.
In classical Rogochover fashion he transfers the discussion to the world of Halacha. A navi must speak the language of the listeners and may not use a translator. That is why Moshe demurred when Hashem told him to speak to Paroh. The only way he would be able to communicate with Paroh would be through a translator and that it not permissible.
2] The Ibn Ezra takes issue with the Rashbam - see there and in the sefer Toras Yaakov of Rav Yakov Chaim Sofer page 112.
3] In parshas Shmos Moshe says that he is כבד פה וכבד לשון while in Vaera he says that he is ערל שפתים. What is the difference?
4] Why didn't Moshe just ASK HASHEM TO HEAL HIM AND PROBLEM SOLVED?? Then Aharon won't have to "pinch hit" [American idiom...:-)]!
לזכות ר' אברהם יצחק בן אסתר ר' יוסף עזרא בן אסתר לברכה והצלחה בכל!!!
