@Crumbly WriterIn Latvian, which is prescriptive grammar language (with a government agency responsible for setting it in law, literally), there's no concept of optional punctuation. Each comma, or lack of one, is eiter correct or in error. That doesn't mean there can't be interpretations of different sentence structures using the same words in the same order, requiring different usage of punctuation. Back in high school I used to write essays with 50+ word sentences, then challenged teacher's interpretation of punctuation errors, with better than 50% success rate of proving different sentence structure with my commas use as valid (even in some cases when in fact the teacher was correct correcting my errors and the alternative I proved possible wasn't what I actually wanted to say). In several occasions those discussions resulted in me and the teacher drawing extensive sentence structures all over the blackboard for half an hour while the rest of the class was quietly doing homework or whatever.
However, that was over thirty years ago. My memory isn't perfect and things change, and I'm not going to look it up, but if I understand what "Oxford comma" is, there isn't one for us.
First, second, third.
First, second and third.
First and second, third.
First and second, and third.
First and second, and third and fourth -- this one is tricky, it implies both first&second and third&fourth are semantically comparable couplings, otherwise one more comma is required splitting one of the couples apart (and potentially leaving ambiguity about the other being a couple or not), and that's possibly the closest there is for an optional comma.
Writing in English, what little I do, I use commas entirely by feel, and overall about 30% less than I would by writing same in my native language, but I think I do use that serial comma more often than not.