Do you know what native speakers look at to determine a person’s fluency in their language?
It’s not proper grammar or even pronunciation—it’s the behavior of the speaker that demonstrates his or her command of the language.
In other words, native speakers are watching your gestures, intonation, courtesies and other behavioral factors to size you up. They are accustomed to foreigners attempting to learn their language, and they are a very observant people.
That is precisely why the best language learning programs teach you to mimic native speakers in every way, from voice modulation to the movement of your mouth and head.
We’ve all known the language learner who has made all As in the classroom and has excellent pronunciation, yet is instantly identified as a foreigner no matter how hard they try to fit in. On the other hand, it is quite possible for a relative beginner to be mistaken for a native if they speak and behave like the locals.
Pronunciation is not heeded (might be from a different region), and neither is grammar (could be a different form where they’re from). No, what matters most in the end is the ease and confidence with which the speaker behaves, while doing a pitch-perfect imitation of a native speaker.
Need proof? Hang around a child. You will hear someone who knows precisely how to speak long before they learn proper grammar and memorize a large vocabulary.
It really is behavior, stupid, so mind your manners too! The importance of good manners cannot possibly be overestimated.