answer:No, nyet, non. Not a good idea. Really. Focus on one first, get the fundamentals and grammar. Without practising speaking it – you won’t retain much anyway. How could one do that with three? Once you’ve mastered two – the third and fourth, especially if they are the same family (say, Germanic) will be easier. French, Spanish and Itralian, par example. But I’m curious as to why you asked this – and what you ultimately do. I teach ESl, btw.