Mormon had been told that there were things that he should not write. The brother of Jared was told that his was a sacred experience, but only a personal one. He was not to tell of the experience. Nevertheless, he was to write it. His record would eventually be available, but only to one who had the tools required to interpret the writing that had been confounded. These tools were two stones, which were kept throughout Jaredite history and kept with the plates of Ether.
These two stones, known as the interpreters, appear to be the ones Moroni buried with the plates for Joseph Smith to find, and, therefore, to have the tools to translate. Nevertheless, they were not the only such tools. When Limhi asks Ammon if there is someone who could translate the plates of Ether that Limhi’s people had found, Ammon tells him: “ I can assuredly tell thee, O king, of a man that can translate the records; for he has wherewith that he can look, and translate all records that are of ancient date; and it is a gift from God. And the things are called interpreters, and no man can look in them except he be commanded, lest he should look for that he ought not and he should perish. And whosoever is commanded to look in them, the same is called seer” (Mosiah 8:13).
Prior to Mosiah having the plates of Ether, and presumably the two stones that accompanied them, he already had interpreters, and had used them. There is no reason to believe that the two stones were the only interpreters, though certainly their sacred provenance would make them preeminent among such tools. The fact that Joseph Smith also had other stones that were used as translating tools confirms that the two stones were not unique, and not uniquely essential to the process of divine translation.