Depending upon the type of school and the program one completes, they can earn a certificate in translation or a degree in translation. A certificate program is shorter in length, maybe only 15 credit hours; whereas a degree program may be consist of 60 credit hours of classes. Is this what you were asking, or did I misunderstand your question?

Unless I'm misundertanding something, just a simple google search turns up "Linguists’ Diploma in Translation", so what you're writing sounds fine. Or maybe a diploma/degree in Language Translation? Providing the context would help if these aren't the terms you're looking for.