Jesus is talking to a group of people about what they as individuals should and should not do. The "you" in "I say to you" is plural. The "you" in "whoever strikes you" and the understood "you" in "turn to him" are both singular, but in some languages they may need to be translated as plural. (See: [[rc://en/ta/man/translate/figs-you]])
Jesus agrees with God and his word, but he does not agree with the way the religious leaders have applied God's word. The "I" is emphatic. This indicates that what Jesus says is just as important as the original commands. Try to translate this phrase in a way that shows that emphasis.
To strike the side of a man's face was an insult in Jesus's culture. As with the eye and the hand, the right cheek is the more important one, and striking that cheek was a terrible insult.