let me hear you say (слэш)

Lan Wangji grew up in a cursed world of silence. People around him say words spoken were more convenient and took less effort than learning how to sign, or to use spiritual energy to communicate. Lan Wangji secretly enjoyed the silent comfort in the knowledge that he can only speak with people he can trust.
Until Wei Wuxian asks a question that confuses him, What language do you speak, Lan Zhan?
...
Lan Wangji learns of languages he never knew to speak before.