There are many movies and TV shows that depict characters from historical eras who would not speak English, but do for the sake of the show's audience. In those cases, they tend to use an old English dialect to mimic how the characters would have spoken in their own language.
For instance, if a movie is meant to take place in ancient Japan, the characters will speak in an English dialect, using English slang and such, even though the people of that era spoke ancient Japanese and didn't use the same slang or have the same accents as the characters in the movie.
Another example would be a show like Spartacus. The characters are either Roman or from tribes in the surrounding areas. They likely would have spoken Latin or Greek, but the characters speak English in a way that sounds ancient, but is clearly not how they would speak during the Roman Empire.
Is there a word for that?