The Berkman Klein Center for Internet and Society at Harvard University has four new publications online.  https://cyber.harvard.edu/node/99716

“Understanding Harmful Speech Online: Research Note” is a summary of current research, with several pages of links at the end.  One phrase that stood out: "Munger also recently conducted an experiment among groups of users on Twitter considered harassers on the platform and found that counter speech using automated bots can impact and reduce instances of racist speech if 'that subjects… were sanctioned by a high-follower white male'.”

Two papers are from the Global South. "Grassroots Perspectives on Hate Speech, Race, & Inequality in Brazil & Colombia" has an entire section on "counter-speech", or counter narratives, a term that seems to be gaining some currency.  "Preliminary Findings on Online Hate Speech and the Law in India" talks about inciting sectarian violence with fake news.

Finally, for an understanding of the definitions of hate speech, forget the Wikipedia article, which embarrassingly uses the words "politically correct" and "Newspeak" in the introductory paragraphs, sourced to opinion pieces by two bloggers who did not even use the words.  The paper “Defining Hate Speech” gives a thought-provoking overview of various approaches to identifying hate speech in a text.  One such framework developed by Parekh noted “three essential features” of hate speech: (1) “it is directed against a specified or easily identifiable individual or, more commonly, a group of individuals based on an arbitrary or normatively irrelevant feature;” (2) the speech “stigmatizes the target group by implicitly or explicitly ascribing to it qualities widely regarded as undesirable;” and (3) “because of its negative qualities, the target group is viewed as an undesirable presence and a legitimate object of hostility.”  Also this, food for thought about criteria for communication on Wikipedia's talk pages: "...Ward’s definition, noting that a speaker should be seen as employing hate speech if 'their attacks are so virulent that an observer would have great difficulty separating the message delivered from the attack against the victim'.”