The conversion of the Jewish nation will be sealed with a great outpouring of the Holy Spirit.
The original prophecy in Joel was given to Israel and its partial fulfillment at Pentecost seems to have been limited to them.
The knowledge of the Lord will be world-wide and "it shall come to pass that ten men of all languages and nations shall take hold of the skirt of him that is a Jew, saying We will go with you; for we have heard that God is with you." Zechariah 8:22-23