abusive friend

What do you do when your partners friend is abusing his girlfriend? 
Like mentally and very controlling. He sees himself as better than better women (I can tell by the way he talks to her and acts around her). 
Her English isn't very good so it's be hard to confront her about it and I feel like it's not my place but Jesus Christ he calls her names and checks her phone daily (they've only been together maybe a month) 
What should I do? Should I say something to my partner about it? 
I'm pretty worried about her and his influence on my partner. 
Help. 

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