Hello. I traveled internationally strictly on business for three months. For meal expenses, can I take the daily IRS mandated per diem for the city I stayed in?

If you are self-employed you can deduct 1/2 of the meals and incidentals portion on your business schedule.  Lodging is deductible at actual expense.

If you are an employee, these are considered employee business expenses and no longer deductible on your federal return.