I almost forgot that the shield has a translation function.
Since it seems that this world has multiple languages, it's quite useful that the shield seems to translate all of them.
As I heard the words in Melromark's spoken language... it seems like it's a language spoken in countries with many humans.
Could it be...
"Well, you don't have to concern yourself with it." [Naofumi]
"Why!? Why would you reject me?!" [Slave]
Like that, we continue to follow the Slave Merchant while ignoring that self-proclaimed slave.