This verse is crucial to understanding the remainder of the Book of Mormon. Much or later Nephite history grew from the seeds planted in this description of the differences between these two peoples who had come from the same place at the same time.
The first is that the people of Zarahemla had been involved in wars and serous contentions. This is Amaleki declaring that the people of Zarahemla were not righteous. The promise of the land was to all who had been led from other countries (2 Nephi 1:5).
The second important point is that their language had become corrupted. That point requires examination. Approximately four hundred years earlier, two peoples left the same place, the same culture, the same religion, and the same language. After that time, they could not communicate with each other. While language certainly changes over time, linguists do not see that amount of time as sufficient to create two unintelligible languages. English has been separated on different continents and has led to different accents and different vocabularies, but not mutual unintelligibility. Therefore, the most likely reason for the mutual unintelligibility is the influence of other languages in the different areas into which the peoples arrived. It is quite possible that the everyday language of the people was that of the surrounding people with whom they had merged.
The idea that they brought no records, and, therefore, there was nothing to prevent language corruption, appears to misread the verse. It does say that they brought no records, but the result of that was that they denied the being of their Creator, not that they couldn’t keep their language. This second change was even more important than the language difference. The religious differences will create a tension that will underlie divisions among the Nephites up until the time of the destruction at the coming of the Christ.