I know this is an SE site for parents dealing with kids... but I am desperate enough for answers, so here it goes.
In summary: I am the daughter. My mother is being domestically abused by my father. What can I do to make him stop without hurting my mother in any way? - she still loves him!
Details: My father is a very abusive character. When I was a child, he used to go into 'rage' modes where he would just beat the life out of my mother. Trying to interfere would only get me enough injuries to not be able to go to school for the next week. As he got older, the rages got fewer but he would still lash out randomly. I'm not talking about the odd slap to the face kind of abuse - I am talking about the kind of abuse that lasts for up to 20 minutes, and renders my mother bloody and swollen and not able to walk for days. Growing up it was extremely painful (physically and mentally) for me and I still wake up from the nightmares. I was terrified of him - I think I've spoken about 15 words with him my entire life.
I moved out when I was 18, reasoning that I could get my mother to come live with me, but she refuses to go anywhere without him.
The last time I went to visit, they started an argument and I interfered and told my dad to back off. He started yelling things at my mother saying she's been training me to go against him, and I wound up backing off at the request of my mother.
I would very much like to file a complaint against him but that would just make things worse for my mother - she wants to be with my father (and I don't understand her) and furthermore, if I do file a complaint, I am sure I will never be able to see my mother again.
I have thought of this so much for the past week that I am hopeless and see no way forward. I even considered paying him some cash every month, almost a bribe to not fight with my mother.
Can you think of any way I can put an end to this without hurting my father's ego so it wouldn't create any more consequences? If only I can find a way to persuade him to not physically abuse my mother...
edit - more info
I moved out to a different country as soon as I could (that's how much distance I wanted between us) and though I now live in a better place, my mother still lives in a third world country where help for cases like this is not readily available - certainly no helpline that I can find online, but a legal action may be a possibility.
During the times when "arranged marriage" was the only acceptable type of marriage, my parents loved each other and, naturally, their parents / family did not agree to that, so they had to do the "runaway marriage" - because of this, neither my mother's family nor my father's family are now in contact with any of us. So getting family members involved is not an option.
Thank you for answering, I was just hopeful that maybe there is a way.. a strategy.. or something I could to to intervene. Looks like professional help is the way to go, though I am scared of that route.