en_tn_lite_do_not_use/mat/12/34.md

You offspring of vipers

Here “offspring” means “those who are like something.” Vipers are poisonous snakes and represent evil. See how you translated a similar phrase in Matthew 3:7.

how can you say good things?

This question can be translated as a statement. Alternate translation: "you cannot say good things." or "you can only say evil things."

out of the abundance of the heart his mouth speaks

Here "heart" refers to the thoughts in a person's mind. Alternate translation: "what a person says with his mouth reveals what is in his mind"