en_tn/act/02/08.md

Why is it that we are hearing them...

Possible meanings are 1) a real question that the people wanted an answer to, or 2) a rhetorical question that expressed how amazed they were. The UDB translates it as a statement showing how surprised they were. (See: rc://en/ta/man/translate/figs-rquestion)

Parthians and Medes and Elamites

"people from Parthia, Media, and Elam." (See: rc://en/ta/man/translate/translate-names)

proselytes

"non-Jewish people who have become Jews" or "converts to the Jewish religion"