The Masked People are the citizens of Facade. They have a unique and exotic language, and welcome Kainé as a friend of the kingdom for saving Fyra.
Information
The Masked People live very differently from the other cities. They are ruled by a king and follow thousands of rules. One of their rules is to always wear a mask, which is where they got their name from. They also speak a different language, which at first is impossible for Nier and Grimoire Weiss to understand, but the latter is eventually able to by comparing Fyra's signs.
Grimoire Weiss's Information
"It appears that there is a race of people who were extremely serious in the distant past. It is said that they would work day in day out in a box of iron and sand. According to the most accurate vocabulary that I know, they are people who are known as "slaves". As a result of their continuous way of living by being serious, they eventually became a race which none of them could live without the guidance of the rules......and they appear to be the distant ancestors of the people of Facade.
However, if you ask me, I think they are simply a group of strange people."
Dialogue
Until the language is translated with the help of Fyra and Grimoire Weiss, the language they speak is always rendered on screen as α☆@&%✻※
.