The word treacherous
has already been used to describe Judah ( Jeremiah 3:8) and it speaks of a failure to maintain the responsibilities of a covenant relationship. Both Israel in the north and Judah in the south are accused of this faithlessness. Mentioning both probably points to the fact that what has already happened to Israel in the north because of her treachery is about to happen to Judah as well.1
11 Car la maison d'Israël et la maison de Juda m'ont été infidèles, Dit l'Eternel.