Leviticus 23:15-16, 21 “And ye shall count unto you from … the morrow after the seventh sabbath shall ye number fifty days; and ye shall offer a new meat offering unto the LORD. …And ye shall proclaim … that it may be an holy convocation unto you: ye shall do no servile work therein: it shall be a statute for ever in all your dwellings throughout your generations.
Fifty days after the Feast of Unleavened Bread is the Feast of Pentecost. Pentecost literally means fiftieth day. This feast is also called the Feast of Weeks because it is also seven weeks following the Feast of Unleavened Bread. It is on this feast day that the Holy Spirit was bestowed upon the apostles and gave them the ability to speak in various languages. The people that were there heard and understood each man in his own language.
Often churches assume that “speaking in tongues” means to recite gibberish. This is not valid. A tongue is a language, as in the statement: “English is my native tongue.”
Acts 2:1-11 “And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language. And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans? And how hear we every man in our own tongue, wherein we were born? … we do hear them speak in our tongues the wonderful works of God.