The Galileans were considered poor, uneducated, and poorly prepared theologically. It was obvious the surprise of the pilgrims when they saw and heard those who spoke such touching words and not in one but multiple languages.
Most of us experience this when we go to another country (either for vacation or business). This is because the country we go to has another language that is not ours.
I only speak two languages, Spanish and English, Spanish being my first language. And to be able, in a way, to handle another language besides Spanish took me years, and I am still learning.
I can imagine the scene when the disciples celebrated the harvest/Pentecost.
Ḥag Shavuot/Pentecost (“Festival of the Weeks”) was originally an agricultural festival, marking the beginning of the wheat harvest. So, many Jews from different parts of the world were there celebrating.