People in the 50s, 70s speak differently from now, why dont more authors or tv shows use fictional accents?

A lot of it boils down to the idea behind what a translation actually means.

One school of thought is that you do word for word translations. So you get very strange sentence structures and direct translations of idioms. Think the idea of (apologies to the French, it has been over a decade since I tried to write or speak any of it) "Il est drole" being translated to "He is to be funny" rather than "He is funny".

The other school of thought is that you care about the meaning of the text and not the word for word translation. So that involves a LOT of updating/adapting idioms but also names. Among the weeb crowd, people lose their god damned minds any time a character has their name changed. But you get into a mess where "Hikari" is not meant to be an "exotic" name and is really being used closer to "Fred".

I remember way back in high school we specifically read a version of Beowulf to demonstrate this. It involved the "original" Old English, a direct translation that is somehow even harder to parse, and then a version written in modern english.

And that is the basic idea. It doesn't matter if Basic is English, Chinese, Russian, or (most likely) a hybrid of them all: What matters is that the reader/viewer understands what is going on and can appreciate the references.

Another example that usually comes up is how the movie A Knight's Tale is one of the most "historically accurate" adaptations ever. Because yes, we have crowds of peasants singing Queen songs and Nike swishes on armor. But... that is a lot closer to what tournaments and jousting were than people playing equally inaccurate classical music. And I've made similar arguments for the god awful Romeo+Juliet where Luigi and Leo wield "sword 9mm" pistols.