Rílin is the language spoken by the Ríli people. It exists in two main dialects, Sunuli and Lunauli. Sunuli is spoken by the Ríli who chose to stay in their original territory after the Flight of many of their fellows to the hidden and subterranean areas in north, due to the recent attacks of the Tosi military. Lunauli is spoken by the Ríli who fled north. These dialects differ mainly in phonology and syntax, but are mutually intelligible.

Rílin is a very fusional language (suffixing), especially in its verbal system. It also has traits of an agglutinative language. The verbal system is ergative/absolutive, and there is a case system for nouns. Different case markers are used depending on how the noun is classified—as an animate or an inanimate.

There are three degrees of familiarity in pronominal suffixes: 1st degree indicates a high degree of familiarity toward the addressee, 2nd a medium degree, and 3rd a low degree. The use and observance of these distinctions was heightened when the Lunauli retreated to the northern woods and the underground caverns and developed a more hierarchical social system, whereas the Sunuli have a more open and lenient social code when it comes to using these degrees.