An original translation
I said, “I’ll start in the same place I did just now, Protagoras, and say what I came for. Hippocrates here really wants to spend time with you. He says he would like to know what he’ll get out of doing that. That’s all we’ve said so far.”
Protagoras responded, “Young man, if you come and learn from me, that same day, you’ll go home better, and the same thing the next day. And every day after, you will make progress towards betterment.”
I said in turn, “Protagoras, what you’re saying is no surprise; it’s only to be expected. Even you, despite your age and wisdom would become better if someone taught you something you happened to not know. So don’t just give us that; think of it this way: say Hippocrates here had a change of heart and longed instead to spend time learning from this young man who’s new in town, Zeuxippus from Heraclea. Say Hippocrates came to him, like he’s come to you now, and heard the same things from Zeuxippus that he has from you: that every day he’s with him, he’d become better and make progress. What if Hippocrates asked further, ‘Now, what exactly will I get better at and what am I going to make progress toward?’ Zeuxippus would tell him, ‘At painting.’ Now let’s say he went to study with Orthagoras the Theban, heard the same things he’s heard from you, and asked him what exactly he’d get better at by spending every day with him, Orthagoras would tell him, ‘At playing flute.’ Now, in the same way tell the young man – and me, since I’m asking for him – if Hippocrates here spends time learning from Protagoras, he’ll go home and be better on the first day he spends time with you and make progress every other day after that, but better in what, Protagoras? Better in what area?”
Protagoras listened to all this and said, “Excellent question, Socrates. I enjoy answering people who ask good questions. If Hippocrates comes to me, he won’t suffer what the other sophists would put him through. They treat young people disgracefully. Their students have managed to escape technical subjects, and then they’re thrown back into them unwillingly when their teachers make them do arithmetic, astronomy, geometry, and music” — here, he looked over at Hippias. “But if he comes to me, he’ll learn nothing but what he came for.”
Compare W.R. Lamb’s 1924 translation at the Perseus Project (Greek text and commentary also available).