בראשית יא, א שפה אחת
ירושלמי מסכת מגילה דף י/א פרק א הלכה ט ר' לעזר ור' יוחנן חד אמר שהיו מדברים בשבעים לשון וחד אמר שהיו מדברין בלשון יחידו של עולם בלשון הקודש
T.T. This is difficult since how did they immediately speak different languages? Further, the preceding chapters said the children of Noach to their families and to their languages לשונם. Thus, it appears that at this time the Holy language (Hebrew) was a general, common language known by all, yet each group of people also had their own particular language. And at the time of the Dispersion, HaShem caused all (except people of Shem) to forget the Holy language, and thus, they lost the common language in which to communicate with each other, Therefore, in the Gemara cited above, the Rabbis did not argue. One Rabbi explained that they all used to speak the one common Holy language, and the other Rabbi explains that each nation also spoke their own language (the number 70 being the standard expression at the time of Chazal).
