A bit of a nit pick on canon, Koume is one of the few who can understand Ranko's speech pattern along with Miria.
Actually, Koume doesn't understand fully. She guesses with fair accuracy.
What does...that mean...?SSR KoumeOohhh!白坂小梅I see you have evolved, Koume my friend!!Now if you'd please, use that fallen angel's bouquet of yours...put it over my head and grant me your blessings!!Hmm let's see...