the language to be used to a baby

What language you choose to talk to your baby is very much a personal choice, but once you have made that choice you should stick to it. You can have one parent using language A and the other using language B and the baby will naturally learn both and intrinsically know which language to use when talking to each parent, what is important is that one person will only ever use one language and never switch and never talk in a mixture (i.e. part of a sentence in language A and part in language B)