There was only one language on earth. In the olden days all human spoke one language because they heard from God. If anyone is deprived of hearing, he won't be able to speak. For one to be able to words correctly, he must hear it constantly.
Hebrews 1:1
God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets.
Adam learnt to speak because God spoke to him so all humans learnt to speak because God spoke to adam
Studies and records have showed that many languages are related,they share the same sound and vocabularies.
God spoke to Abram in
Genesis 12:1
Now the Lord had said unto Abram, Get thee out of thy country, and from thy kindred, and from thy father's house, unto a land that I will shew thee.
God appeared and spoke to Abram again in
Genesis 17:1
And when Abram was ninety years old and nine, the Lord appeared to Abram, and said unto him, I am the Almighty God; walk before me, and be thou perfect.
Deuteronomy 4:6,
God instructed the Israelites to keep his commandments.
Most nations around the world have adopted these commandments of God for their Constitutions,like thou shall not steal, thou shalt not kill and some more and this proofs that these commandments came from God almighty.
We all learnt how to speak from hearing.
Thanks you brethren and may God bless you all