Mickey you should totally speak to Juleika in German, now is when babies are learning language and people who speak more than one language have got a great advantage in today's world. I'm trying to let Kaya hear as many languages as possible atm.
I did some research on this and they said you should not mix them up, but you should set certain areas were you speak only one language to them, otherwise they might get confused.
e.g.
mummy, daddy + Juleika = english
mummy + Juleika = english (helps if I need to go to doc and so on...)
mummy + friend + Juleika = german
mummy singing and reading = german
I try to speak as much german with her as possible, e.g. reading, singing, playing german children song, meeting up with german friends, talking german on the phone, searching for german toddler groups and even possibly attending a german saturday school when she is older (depends if we are still living here, as here we would have one available)
I will def support her learning german at most
fact is the daughter of a friend of mine, who is now two and a half and heard four languages from birth on, still can only speak a few words.
as well I heard from the experience of people that those children are able to speak all language fluently, but sometimes have problems to express themselves correctly. may be, 'cos every language has several layers, if you e.g. even take dialects into account
my english vocabulary is missing out on slang, but it's improving