What do you mean by "simply" though... Some people suggested not to use any words with more than a few syllables. Let me translate the last post into this few syllables scheme.
original post by James:
"That's a possibility. In that case grammar errors would be required, but it would be exceedingly difficult for a native speaker to imitate the interlanguage of a learner so the rules requirement would just be "make some grammar errors". I personally would prefer to just speak simply (but accurately)."
My translation into "simple":
"That could be. In that case grammar errors would be needed, but it would be very hard for a native speaker to sound like someone just learning the language so the rule would just be "make some grammar errors". I would prefer to just speak simply (but still clearly)."
That doesn't sound like a barbarian at all to me. The longest word in the above text is 3 syllables long "language" and possibly "someone". The rest are all 1 or 2 syllables. And I don't think that the meaning is lost in any shape or form. So using small words doesn't actually make you sound any different. It might just make you sound like you have a small vocabulary. Definitely not to the point of "Ugh, me found shinies, me like shinies. Me give shinies to you, you give sword to me?" But that's always sounded more like caveman to me than barbarian.
If you listen to non-native speakers, you'll notice that verb conjugation, placement of adjectives and sentence structure are more likely to be wrong. They won't sound like complete idiots, but they might say something like "I would likes the drink of water" instead of "I would like a drink of water".
Anyways, to each his own.