Yes, yeah, no, and nah

One thing that is easy to notice about English is that we get pretty lazy when we speak certain things. What really comes to mind for me is 'yes' and 'no'. We have the proper 'yes' but we also lazily say yeah and ya, for example. Instead of 'no' we sometimes say nah (for some reason I don't include 'nope' in this, but maybe that's just me). It isn't a dialect thing as much as it has to do with what register you're using, in my opinion.

I've had some Italian and it seems I only ever see or hear, in class, writing, or movies, 'sì' and 'no'. Seems like no deviation.

I am not exposed to many other languages, but is what happens in English very common as far as world languages go?