How to Best Help
I suggest you ask around at the courthouse. You might need to get advanced permission from the judge. Every courthouse is setup a bit differently so it's hard to say exactly whom you will need to ask. But ultimately that will probably require the judge's advanced approval.
Order of Child Support
You used the term violation so I will assume the mother has in her possession a copy of the Order of Child Support (OCS) resulting from the divorce or paternity case that determined the amount and timing of support payments she is entitled to. Correct?
Aside: If the mother doesn't already have an OCS it's pretty simple to get one. Most states just have a standard set of forms and a formula to apply. There is very little subjectivity involved. Unless one or more of the parties has unreported or variable income. And she can also collect back child support too.
Back Child Support
AFAIK you are not barred by statute for seeking back support as far back as when dad's obligation began. Which AFAIK is when mom became the primary caregiver. In practical terms, this would be the first day mom had the kids living with her and dad didn't live with them.
Interest on Unpaid Child Support
Most states allow mom to collect interest on (ordered but) unpaid child support at a rate set by statute. In some states the interest rate is in the 9 to 12% range. You need to compute it using a spreadsheet. You go back to each ordered monthly obligation, calculate the number of months from then until the current date, then multiply that number times the obligation amount times 1/12 of the interest rate. Then add all those months together to get the total. Like I said, a spreadsheet is the easiest way to do this calculation.
Motion for Contempt of Court
Assuming you have acquired an OCS, enforcement is also pretty straightforward. In some states, the mechanism to force the father to pay is called a Motion for Contempt of Court for violating the OCS. Again, it's so common, unfortunately, most courthouses support pro se litigants by having all the necessary forms on hand and volunteers to help people fill them out! When mom files the contempt motion with the court she will schedule a date for a Show Cause Hearing, at which time dad will need to appear and explain why he should not either pay up or be found in contempt of court. Courts enforce child support VERY strictly. So the paperwork alone should be enough for her to win her case.
Unlicensed Practice of Law
As for you "helping her" in court. Be very careful. That sounds dangerously like practicing law without a law license. There is a thing called a "bar" in the courtroom that only attorneys or clients are allowed to cross (by practice and tradition). That's where the term bar exam originated. Anyway, if you want to try that, be very careful and you might want to run that by the judge or clerk and get prior approval first because the unlicensed practice of law has the potential to be a sticky wicket.
Use of an Interpreter
I would be shocked if the court did not make allowances for non-native English speakers to use the services of an interpreter in the courtroom. That's something you definitely need to ask around at the courthouse for all the details. And whether the interpreter needs to be licensed, registered or otherwise approved by the court in advance.
One last point. Make sure to properly process serve dad with the motion and paperwork. Process service is what will bind him to appear at the show cause hearing. You should be able to find forms, instructions and a professional process server by asking around down at the courthouse.
Dad will have a chance to respond in writing to the motion prior to the hearing. And mom will have a chance to respond to his response. Ask around at the courthouse how all this works. Especially the deadlines involved. These are also strictly enforced.
State Registry Enforcement Assistance
One last, last point. In the future, it might help if the OCS made a provision for the father to pay directly to the state registry for child support enforcement. The will keep track of all the payments and can provide enforcement assistance like levying bank accounts and garnishing wages, etc. So that could help with future enforcement.
I am not a lawyer. I am not your lawyer and you nor the mom are my client. This is not legal advice. So please don't do anything based on what I write here; if you do, please be aware you do so at your own risk. So seek the advice of a real lawyer if you are going to actually do anything that might create an issue.