English is Blake’s second language. There is a language the Faunus used to know but it’s rarely heard outside of Menagerie, that’s Blake’s first language. Her parents taught her both as she was growing up so things would be much easier for her, and she can speak both fluently.
There’s times she’ll stumble, but they’re very rare. And they’re usually if there’s a word she’s thinking of that she knows in her native language but there’s no English alternative for it.
Bonus; RW_Y actually discovered this through Blake sleep talking. Ruby remembered a few phrases and asked her what they meant and Blake was kinda embarrassed it was things like “But mom I already did the chores.”