It's fairly obvious that English is slowly but constantly invading our space, which is not really surprising given we're in England.
BK1's mother tongue is now clearly English. I guess it was inevitable. We shall see what her 5 week stay in Algeria in July will do, but for now there is no doubt.
BK2 picks up everything people speak her way. She happily replies to Souad in Arabic or French, to me in German and to other people in English. Or at least she tries.
Between BK1 and BK2, things are not clear. When they play, BK1 will use English, but when she addresses BK2 for something, she'll use French or Arabic. My guess is that the summer holidays will change this, like they did last year.
And maybe some German will creep back into the picture at some point. I hope.