Moroni understands, and declares, that “none other people knoweth our language.” Moroni understands that it would come forth in translation. The only hint that he understood that process was his statement that “the Lord knoweth the things which we have written.” Moroni trusted that God’s knowledge would support the translation of that unknown language.
The Book of Mormon was written with a purpose, and by inspiration. The positive message was that future generations would believe in the Lord, Jesus Christ. However, one of the responsibilities that Mormon and Moroni shared was to preach the gospel. They did that in the Book of Mormon. Thus were “these things … written that we may rid our garments of the blood of our brethren.” They have fulfilled their responsibility to do what they could do to assist in the final gathering of the New World house of Israel.