Meridan

The Exodus language. Exodus Lullabies are written in this.

Should probably figure out whether it's Meredan or Meridan, it's Meredan in this back of the book segment:

Arii and alet, interestingly enough, are not loanwords from the Seersan tongue, but from Meredan, the Exodus language. This was a pidgin that began formation on Earth, where it was used by the Pelted (before they were called the Pelted) to communicate with each other without being understood by their owners. Meredan did not become a full language until after the Exodus, but its heyday was brief—it was used on-ship and then fell out of use in favor of Universal not long after the first settlements. The reason for that abandonment is still hotly debated today; you will find many academic dissertations on the topic if you browse a Pelted library in the historical linguistics section. The most popular theory is that its association with victimhood and powerlessness made it less popular than Universal, with its implication that the Pelted were free to use the language of their oppressors without fear of retribution. But no one’s sure why Meredan use dwindled, and to this day its study remains an eccentricity particular to scholars. The few words that have survived in the Universal lexicon are assumed by laymen to have been borrowed from Seersan.