Redaction: This verse explains why Mormon reported that Ammon read Zeniff’s record: it introduces the question of interpreting other written documents. Zeniff’s plates bridge the action between Ammon’s interest in Zeniff/Limhi and this revelation of new records.
It is possible to reconstruct some of Mormon’s source. After the public meeting, Ammon and Limhi go to the king’s residence, and Limhi gives him the history of his city’s founders to read. Because this history is on plates, Limhi remembers another set of plates that his people found but which they cannot read. He asks Ammon whether he can interpret languages. Although we can deduce Limhi’s mental association from what happens next, it must have been an unexpected question for Ammon. This suggests that Mormon’s source is reporting a conversation with reasonable accuracy. Therefore, Mormon, despite his abridgment, is preserving the sequence of events in the original.