Sorry, There is no Oxford Comma in German.
Discussions begin, lawyers are called, and lawsuits are filed. All of it is about a comma. (See what I did there?)
The Oxford comma is so important to people that spouses actually have discussions about it. They've talked about everything like where to live, how to manage their finances, and how many kids to have, but years later they find out only one of them uses the Oxford comma. [Cut dramatic music.] It's like now the real stuff of marriage has come to the forefront:
to use the Oxford comma or not?
In English class I was taught the following: when you write a list of three or more items and the list needs differentiation, or might sound confusing, then you insert the comma before "and." Ergo:
Maria asked Bartholomäus, her teacher, and husband if she should use the Oxford comma.
In this sentence, Maria is asking three separate people: Bartholomäus, her teacher, and her husband, whether or not she should use the Oxford comma. Writing this sentence without the Oxford comma leave interpretation open, so it might mean that Maria asked three people, or it might mean what we discover in the next sentence.
Because without the Oxford comma, we find out something very interesting about Maria:
Maria asked Bartholomäus, her teacher and husband if she should use the Oxford comma.
namely, that Bartholomäus is her teacher AND her husband. (Oha!)
Tut mir leid, aber...
In German there is no Oxford comma. So when Maria goes to these three people to ask her question, there is no comma for differentiation:
Maria hat Bartholomäus, ihren Lehrer und ihren Mann gefragt, ob sie das Oxford-Comma verwenden soll.
Here the accusative case helps you differentiate that Maria has asked three different people the same question. However, you might not catch it on first hearing or reading. In that case, confusion requires one more step: nachfragen. Ist der Bartholomäus denn ein Freund, oder auch ihr Lehrer und/oder ihr Mann? Gute Frage!
It's really hard to remember this rule, especially when you switch back and forth between German and English often. So be sure to review your German texts when you've written a list und entfernen Sie das Oxford-Komma!
*The Oxford comma is also known as the serial comma.