Even if they don't get it quite right, it helps put you in the "head" of another time.

What ticks me off is when they speak in phony accents to remind you the characters are not speaking English. If you are watching a room full of Nazi generals, you don't need to be reminded they're speaking German. And nothing sounds sillier than the "Biblebabble" they put in the mouths of the characters in Bible movies so they'll sound authentic. In "The Last Temptation of Christ", all the characters speak in colloquial, ordinary, American-accented English, even though presumably they are really speaking in Greek, Aramaic, Hebrew or Latin. It works. In "The Passion of the Christ", Mel Gibson has the characters speaking in Aramaic and Latin and the subtitles are printed in English below. It really makes you feel like you're really there.

In movies like "Robin Hood", everybody adopts this silly medieval English speech, even though the English language didn't even exist then. The Merry Men spoke Anglo-Saxon, and the Sheriff of Nottingham and Prince John spoke Norman French. All the characters were probably fluent in both. Modern English and French speakers would not understand either.