“So” is indeed one of those small things that’s just colloquial to casual conversation in in Germany. To me personally it signals that you weren’t as exact with your question so you’re leaving it kinda open ended to some degree. But when it comes to Grammar no clue what this is.

It feels a bit similar to “do you speak any other languages or ~” because this leaves it less as a direct question and more as an open ended conversation, suggesting you just wanna know more and you’re not very particular in your question and in what you expect as an answer.