The following is A.T. Robertson's comment on Matthew 3:2 from his Word Pictures in the New Testament. Robertson underscores the fact that the word "repentance" is a tragic mistranslation of the Greek word metanoia.
"Repent (metanoeite). Broadus used to say that this is the worst translation in the New Testament. The trouble is that the English word “repent” means “to be sorry again” from the Latin repoenitet (impersonal). John did not call on the people to be sorry, but to change (think afterwards) their mental attitudes (metanoeite) and conduct. The Vulgate has it “do penance” and Wycliff has followed that. The Old Syriac has it better: “Turn ye.” The French (Geneva) has it “Amendez vous.” This is John’s great word (Bruce) and it has been hopelessly mistranslated. The tragedy of it is that we have no one English word that reproduces exactly the meaning and atmosphere of the Greek word. The Greek has a word meaning to be sorry (metamelomai) which is exactly our English word repent and it is used of Judas (Matt. 27:3). John was a new prophet with the call of the old prophets: “Turn ye” (Joel 2:12; Isa. 55:7; Eze. 33:11, Eze. 33:15)."
For more information on metanoia, see The Great Meaning of Metanoia.