Few punctuation marks can spark as much passionate and fervent righteous indignation as an omitted Oxford comma.
You don't believe me? Entire webpages are dedicated to arguing for its usage. Memes are plentiful. Examples can be found here, here, and here. Thank you, dear reader, for permitting that brief moment of rebellion.
You divisive little so-and-so.
For those of you who are learning the English language, the Oxford Comma is the last comma in a series before a conjunction. For example, the final comma in: Tom, Dick, and Harry. So is it strictly necessary to use the Oxford Comma in all cases? Not really. There are some cases, however, in which it helps to make things clearer. For example, if I dedicate this article to "my parents, John F. Kennedy and Jacqueline Kennedy," it may sound like I am claiming that the latter are in fact my parents (which would, of course, be incorrect).
However, that is not the main reason I use the Oxford Comma in all of my work, whether translation or editing/proofreading. The reason has to do precisely with the comma enthusiasm discussed above. I have no interest in judging the writing, the style, etc. of my clients. However, it is very important for translators and editors to understand the potential pitfalls in the target language. Moreover, we need to know what language and terminology is socially acceptable, and which is considered outdated, or even offensive to some readers.
How does one do this? Recently-published papers on a similar topic from a official or reliable source. The best advice I can give is to pay close attention and listen. Pay attention to what you read and see in the news, and yes, even social media. The latter especially is an extremely fallible source, but it is helpful for recognizing red flags in a fast-changing cultural lexicon.
So she's saying always play it safe?
Not necessarily! The most important thing to remember is this: readers will remember the client's name, not the translator's. I have no right to enter my clients into a polemic situation that they did not consent to being in.* Even if I do not think the Oxford comma is necessary in a given sentence, I still include it to save the client from unnecessary judgment.
Having said that, there are times in which the client deliberately wants to make a strong statement or an unconventional choice, and the translator must respect that desire as well and render it faithfully. When in doubt: ask. Make sure the client is aware of how a word or phrase will be perceived in the target language and that they are aware of any risks involved.
Ultimately, it is not the task of the translator to judge the text that is presented to her, but it is a central part of her job to know how readers in the target language may judge it.
* Once considered a grammatical transgression of a similar magnitude to the omission of the Oxford Comma, ending a sentence with a preposition is becoming more acceptable, and Merriam-Webster agrees.