See Bereishis 41:45. Ramban suggests here and in Bereishis 45:12 that Pharaoh knew Hebrew. Rashi to Bereishis 50:6 (quoting Gemoro Sotah 36b) says that Pharaoh made Yosef swear he would not reveal that Pharaoh couldn’t speak Hebrew. See Ramban on Bereishis 47:31.
It could be that although he might have been able to understand it somewhat and even speak a little of it, however he was not capable to converse in it. The Gemorah Sotah 36b, says that when Yosef spoke to Pharaoh he couldn’t answer him.