In one embodiment, a method includes receiving, from a client system associated with a first user, a first user input by the first user, wherein the first user input is associated with a current dialog session, identifying a first language register associated with the first user based on the first user input, accessing a plurality of language-register models associated with a plurality of language registers stored in a data store, selecting a first language-register model from the plurality of language-register models based on the identified first language register, and generating a first communication content responsive to the first user input, the first communication content being personalized for the first user based on the selected first language-register model.