In Vulgate, Matthaeus 4:23, it says "et prædicans Evangelium regni". Shouldn't it be "regno" (dative) rather than "regni" (genitive)? He was talking the gospel TO the kingdom, not the gospel OF the kingdom.
The Latin is a pretty literal translation of the Greek:
καὶ κηρύσσων τὸ εὐαγγέλιον τῆς βασιλείας
"τῆς βασιλείας" (tēs basileias) is genitive, not dative. He is preaching the Gospel of the kingdom, not preaching the Gospel to the kingdom.
This makes sense. The "kingdom" in question--as is clear from many other passages throughout the New Testament--is the "kingdom of Heaven" (ἡ βασιλεία τῶν οὐρανῶν) or (as Mark and Luke prefer to say) the "kingdom of God" (ἡ βασιλεία τοῦ Θεοῦ). It is the message, not the recipient.
A review of several English translations makes it pretty clear that this hasn't been a matter of dispute.