Other mistake: Arabic inscriptions can be seen on the golden desk, but the letters aren't connected like normal abjad. This is likely a computer rendering error since some editing software don't natively support foreign characters. (00:17:10)
Plot hole: When Vlad enters Mehmed's tent, the entire floor is covered in silver coins and Mehmed remarks on Vlad's weakness to it. There's no way that Mehmed could have known about Vlad being a vampire or about his weakness to silver, as Vlad had killed every Turk after becoming a vampire, so nobody would be alive to tell him. Even the Turk found on the battlefield in the morning lived long enough only to deliver Vlad's message, but died immediately after that.