Groghor was a language originating on the northern continent. The native speakers of Groghor were wiped out during the Lady's consolidation wars of her Empire. This occurred sometime during the roughly 4 decades which preceded The Black Company. As a result of the Lady's conquest, the language was on the verge of extinction by the time of the Books of the North.
Murgen, the Annalist of the Black Company, had learned Groghor from his maternal grandmother. After joining the Company he only used the language to cuss people out. He mentioned the language in his Annals (Bleak Seasons). Lady read his chronicles, and remembered the detail. Unknown to anyone but herself, she was also one of Groghor's few remaining speakers. She had a private conversation with Murgen in Groghor during She Is the Darkness. She informed him that the apparition of Kina they had seen had actually been a trick orchestrated by sister Soulcatcher. Soulcatcher did not understand Groghor, so even with spies, their conversation would not be understood.