Out of curiosity, let's assume that our character just doesn't quite break the border on the language barrier, you make a new dude, whatever. Let's say he's from Italy, Germany, France, Mudda Rusha, you get the idea.
Now, let's assume he's German.
Ye?
And he meets a Falkovnian. Now, of course, Falkovnian is not-German for Core people, but everyone will go, "Ja, bitte," if they say, "Yes, please," or... "Scheiße!" for their more coarse language. Let's say you're playing this German, and of course, his native tongue gets peppered in with, or completely is used in lieu of common.
And you walk down the road, you're interacting with someone, and a Falkovnian player walks up.
"Hallo! Wie geht's dir?" If he's super-dedicated. There's immediately an incredibly awkward moment of either, "Yes, we're using the same Real-Life language, but mine actually represents my fake language that's using German as it's linguistic representative."
It's not incredibly conducive. Similarly, let's just say we play an old-school Russian or Romanian. Everyone's going to think you're a local at a glance, even if you're an Outlander. Seems like it'd lead to a lot of awkward... "[Tell] I'm actually a German/Russian/Romanian, from GE. Not a local. You don't know what he's saying."
What is the official ruling on how to make this less complicated? Because theoretically, they're not even the same language. Unless somehow they have similar roots and it's ruled that they can roughly understand each other.