It's implied.
Paul was born in Turkey in the very heart of Greek thought and philosophy, Turkey at the time was at THE center of Hellenist culture and influence (Hella - Greek/Greece), he speaks with a heavy political/commercial manner of greek terminology when addressing an audience, has extremely high knowledge of greek poetry and beliefs (for a non-secular Hebrew).. even when he asked to speak to a multitude of angry Jews the Chief asked him "aren't you that Egyptian?" which may be reference to Alexandria Egypt where the Greek influence began. The chief asked "don't you speak Greek"?
Paul is then given license to speak to the Jews in Hebrew. They listen to his speech with open ears as they hear him speaking the Hebrew tongue.. he explains where he was born and where he was sent to at a young age to study Hebrew and Law under Gamaliel (who taught in Jerusalem).... So Paul who is a Jew, a Roman citizen and soldier, raised in a heavily Hellenized jurisdiction, spoke Greek, well studied in greek philosophy/poetry and then studied Hebrew Law in Jerusalem at Hebrew academy (btw the Temple priest in Jerusalem required Hebrew, Jerusalem was Hebrew orthodoxy, not under Greek control since the Maccabean revolt and rededication of the Temple) ....aaaaaannd he was a Christian an Apostle of Christ..
Greek was beyond a doubt the most likely first language of Apostle Paul before moving to Jerusalem and learning Hebrew dialect at a young age
For the multitude of the people followed after, crying, Away with him. And as Paul was to be led into the castle, he said unto the chief captain, May I speak unto thee? Who said, Canst thou speak Greek? Art not thou that Egyptian, which before these days madest an uproar, and leddest out into the wilderness four thousand men that were murderers? But Paul said, I am a man which am a Jew of Tarsus, a city in Cilicia, a citizen of no mean city: and, I beseech thee, suffer me to speak unto the people. And when he had given him licence, Paul stood on the stairs, and beckoned with the hand unto the people. And when there was made a great silence, he spake unto them in the Hebrew tongue, saying, Men, brethren, and fathers, hear ye my defence which I make now unto you. (And when they heard that he spake in the Hebrew tongue to them, they kept the more silence: and he saith,) I am verily a man which am a Jew, born in Tarsus, a city in Cilicia, yet brought up in this city at the feet of Gamaliel, and taught according to the perfect manner of the law of the fathers, and was zealous toward God, as ye all are this day.
Acts 21:36 - 22:3