Despite a fair amount of Turkish being spoken throughout the movie none of the actors are Turkish or have Turkish language backgrounds. Therefore they have different accents even though their characters are native to the language.
Mehmed first defeated Vlad (Vlad Tepes) in 1462 and Vlad fled to Hungary and prisoned until he released in 1474.
In 1476 he attacked to Ottomans and defeated again but this time Vlad's head was brought to Mehmed as a proof. Mehmed died 5 years after he defeated Vlad III for the second time. After he defeated Vlad III he put Radu in that position and the region was still a part of the Ottoman Empire till 19. Century.
Vlad III was not known as Vlad the Impaler during his life, but was rather given the nickname posthumously. Therefore, he would never have been called this by anybody, as he is several times in this movie.
When Vlad enters Mehmet's tent for the last fight, Mehmet says, that Vlad has a problem with silver. He could not know that, as no turk has survived a fight with Vlad to tell that, since he turned into a vampire.