yeah, and i'm sure that when you where reading about python or javascript you were like.. ohhh so that's why i was doing this and that on php or java.. that's what i mean, comparing and relating helps to learn :D
you are right, and i still don't master any language. my point is that for someone trying to learn by himself, it may result useful to use several languages, because making comparisons and relating concepts helps to understand things. at least it helped me.