Which Old Testament translation did Calvin use?

The Reformers all knew Greek very well. Not all of them knew Hebrew as well, but Calvin knew Hebrew.

Something we miss sometimes is that Calvin spent time at Strasbourg. Strasbourg was the home of probably the best exegesis that was happening during the time of the Reformation. The Hebrew work that underlies Luther’s work—in terms of the scholarship and Hebrew grammars—was coming out of Strasbourg. This is also true of the city of Basel, and Calvin spent time there.

So Calvin knew his Hebrew, and he knew his Greek. You see him using his Hebrew in his Old Testament commentaries. But as a general rule, the Reformers knew their Greek better than they did their Hebrew.