Greek:

ἀλλ' ὅτε εἶδον ὅτι οὐκ ὀρθοποδοῦσιν πρὸς τὴν ἀλήθειαν τοῦ εὐαγγελίου, εἶπον τῷ Κηφᾷ ἔμπροσθεν πάντων, Εἰ σὺ Ἰουδαῖος ὑπάρχων ἐθνικῶς καὶ οὐχὶ Ἰουδαϊκῶς ζῇς, πῶς τὰ ἔθνη ἀναγκάζεις Ἰουδαΐζειν;

KJV:

But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?

Darby:

But when I saw that they do not walk straightforwardly, according to the truth of the glad tidings, I said to Peter before all, If thou, being a Jew, livest as the nations and not as the Jews, how dost thou compel the nations to Judaize?

DBH:

But, when I saw that they were not proceeding straightforwardly regarding the truth of the good tidings, I said to Cephas in front of everyone, “If you who are a Judaean live as a gentile and not as a Judaean, how is it you require the gentiles to become Judaean?”

Gloss:

But when I saw that the baptized Jews in Antioch—even Peter and Barnabas—had pulled back from sharing meals with baptized gentiles, a practice that had been agreed upon in Jerusalem among all the apostles and elders (including James, Peter, John, and Barnabas), I said to Peter before the whole assembly: “If you, as a Jew, mix readily with gentiles at the table, sharing meals with all the baptized, irrespective of lineage, and (until now) refused to keep yourself to table fellowship exclusively with Jews, why would you change policy by suddenly requiring gentiles to Judaize—that is, to come to the exclusively Jewish table through circumcision and kosher—when, if they were to imitate this new policy from their side, they would simply keep to themselves as you do? In other words, you, as a Jew, once went to them, as gentiles; why do you now force them to come to you, not as gentiles, but as Jews?”