My bro ( and late dad had)the ability to switch easily between English and German. Pre retirement bro career was a business person so all thought was in German. I've never asked him about dreaming! Unfortunately the linguist gene by passed me, I found German easy first year of GCE, then got bored and gave up, French hard at first, got easier, gave up. I was clearly fairly intelligent, we all went to Grammar School, but unlike other family members I didn't do uni after A levels. I regret not appreciating the good education I got, but it did stand me in good stead during my career when I finally got 'it' out of my system ( ie good times late 70s/ late 80s) before I got serious about life and work. I did OK, but never did bother with the languages!