Although painful, your situation is not uncommon. It’s not unusual for parents who don’t speak English to turn to their kids to be translators. Unfortunately, the more the parents depend on their kids, the less practice they get in the language. The problem therefore continues.
You are under no obligation to be your mother’s counselor, translator and emotional support. She is the mother. You are the kid — even though you are 17. If your mother and her boyfriend can’t solve their problems, they need to see a professional, not you. You have enough to deal with in your own life. But withdrawing from your role as translator/counselor is easier said than done.
It will be easier on you emotionally if you don’t feel like you are abandoning your mom but are instead turning the problem over to someone else. I suggest you research whether there are services in your city that provide translators and English lessons to immigrants. Also look for bilingual counselors. If there are no services, consider whether there is an adult friend or relative who you can enlist to be your mothers’ support person.
Once you identify some supports, I suggest you tell your mother and her boyfriend that you are not trained to be a good help with their problems with communication or with their relationship. Give them the resource numbers and tell them you can’t and won’t do it any more.
This will be difficult. You may need to figure out an “exit plan” when they start fighting. Think about places you can go (a friend’s house? the library?) when they start arguing. Get yourself some earphones and use them if you have to stay home.
Do not let anyone try to make you feel guilty for withdrawing your help. If anyone tries, simply tell them the truth: You are not a trained professional and there is a risk you will do more harm than good if you continue to try to solve your mom’s problems. The best help you can give her at this point is support to find real help.
I hope your brother is working with you to help your mom transition to more independence. It will be helpful if he will add his voice to yours to get you out of the middle.
I wish you well.