5. Pretty much everyone understands every language
On Earth, today, there are over 6,000 spoken languages by humans. That's a lot of people unable to understand a lot of other people. Now pretend that, instead of all of the people being humans, they're a mix of elves, and dwarves, and floating jellyfish. It's safe to say that each of those races could potentially have 6,000+ languages of their own, right? Now… why can your character in [insert fantasy or sci-fi game here] speak and understand the language? Why can they understand yours? Magic? Science? Laziness?
Another question: do you care? Because I don't. Sure, it's unrealistic, but not being able to understand someone is frustrating as hell. Talking to the King of Goblins would require you to communicate through charades or via a translator, neither of which are any fun. I mean… it might be cool for a second, but as soon as I need to repeat a level because my in-game translator mixed up the words for "spend the night" with "sleep with your daughter" I'm done with gaming. I'll just move on to, like, knitting or something.