What does Victor study after his illness as a means of keeping his mind busy?

Victor Frankenstein has experienced what he calls a "nervous fever." He seems prone to such disorders, especially in the wake of traumatic events. The night before, he'd successfully completed his life's work—the creation of the Monster; but the beauty of his dream immediately gave way to horror and disgust. Under such trying circumstances, it's little wonder that Victor should experience a nervous breakdown.
Thankfully, however, Henry Clerval is on hand to act as nursemaid and companion to his stricken friend. Although Victor suffers one or two relapses, he eventually recovers, in no small measure due to Henry's kind ministrations. As he recovers his strength, Frankenstein needs to keep his mind busy, to satisfy his innate craving for intellectual stimulation. Science is out of the question, as Victor now cordially loathes his former studies. So he follows Henry's example and engages with the study of "Oriental" languages such as Persian, Arabic, and Sanskrit. He doesn't attempt to gain any in-depth knowledge; he just wants to pass the time. But he does find the study of these languages rather soothing, bringing him some much-needed joy amidst all his various troubles.