Genesis 39:4

He made him overseer over all that he had Committed all to his care and management. But it may be asked how this could be, since Joseph understood not the Egyptian language? In answer to which it may be observed, that, undoubtedly, as soon as he came thither he would do his utmost to obtain the knowledge of that language, and being a person of good parts, would soon obtain it, especially as there was a great affinity between that language and his own. Besides, it is not to be supposed that Joseph was highly advanced at once, but step by step, and after some considerable time. For, considering Potiphar's office and station, it is not likely that he would thus prefer Joseph till he had had full evidence of his fidelity, as well as of his ability to manage so great a trust.