Ibn Ezra on Gn 11:6, 7

ONE PEOPLE. They have one religion. Different religions create jealousy and hatred among people. The same is true with regard to different languages. That is why the king of Persia and Media commanded that every man should bear rule in his own house, and speak according to the language of his people (Es. 1:22). The heh of hachillam (what they begin) is vocalized with a pattach because of the chet which follows it.

[AND THERE CONFOUND THEIR LANGUAGE.] All the grammarians claim that ve-navelah (and confound) is a nifal. They compare it to ve-navekah (and shall be made empty) in And the spirit of Egypt shall be made empty (ve-navekah) (Is. 19:3) and to navelah (fadeth) in The earth fainteth and fadeth away (navelah) (Is. 24:4). However, their interpretation is farfetched. Why would the Bible say: Come, let us go down and their language will be confounded, when their language was not confounded because God and the angels went down? Ve-navelah can only be interpreted as an active verb. Proof of this is Scripture’s stating at the close of this incident, because the Lord did there confound the language of all the earth (v. 9). The following is then the grammatical explanation of ve-navelah. It is a hifil. Scripture should have employed the entire root and read ve-navlilah, or ve-navellah if one of the two lameds of its double root was swallowed. In the latter case it would have followed the paradigm of ve-nasebbah (let us bring back) in and let us bring back (ve-nasebbah) the ark of our God (I Chron. 13:3). Our word reads ve-navelah because one of the lameds of the root was dropped without the remaining lamed receiving a dagesh forte to make up for it. The sages who translated the Torah into Greek correctly rendered ve-navelah as I will confound, rather than we will confound. If the above mentioned grammarians are correct, why did the sages omit the nun? Some say that the people building the tower started hating each other and each one invented a new language. Others say that the One who grants knowledge to man caused them to forget their language. In my opinion, they were first scattered. After their dispersion Nimrod ruled over Babel and other kings arose. With the passage of time and the death of the first generation to be scattered, the original language was forgotten. God scattered the people for their own benefit. He similarly said, and replenish the earth (Gen. 1:28).