Acts 21:37 & 38

"As the soldiers were about to take Paul into the barracks, he asked the commander, 'May I say something to you?' 'Do you speak Greek?' he replied. 'Aren't you the Egyptian who started a revolt and led four thousand terrorists out into the desert some time ago?'" NIV translation

As Paul was being taken into the barracks, he spoke to the commander in Greek which surprised the commander. The commander did not know Paul and did not recognize him but instead thought he was a common criminal. This speaks much about Paul and his ministry in that it was all about Jesus and not self promotion. 

Today, there are many that are peddling the gospel for fame and profit but Paul was simply led by the Holy Spirit and shared the gospel.

Acts 21:39 & 40

"Paul answered, 'I am a Jew, from Tarsus in Cilicia, a citizen of no ordinary city. Please let me speak to the people.' Having received the commander's permission, Paul stood on the steps and motioned to the crowd. When they were all silent, he said to them in Aramaic:" NIV translation

After Paul cleared up the case of mistaken identity, he received permission to speak to the crowd. He had spoken in Greek to the commander but switches to Aramaic to speak to the Jewish people.