I think what copperx is talking about, and certainly what I was talking about is not your ability to speak and communicate at a native level in the languages you speak, but your inability to achieve a very high level of competency i.e. talk with the clarity of a Steven Pinker or Noam Chomsky or generally anyone you consider to be highly articulate. IMHO this is largely due to actively speaking multiple languages on a daily basis. Its wierd because I can&#x27;t really explain the types of mistakes but its things that second language learners won&#x27;t ever do, like starting a sentence in one language and finishing in another, or adopting a verb from one of the languages you know, for instance in DE&#x2F;EN, &quot;gimme den ball&quot; or &quot;er hat gesagt he&#x27;s sold.&quot;. It requires active concentration to not do this and can often lead to slight pauses where you are searching in your head for the X language equivalent of the term in language Y (only then to realize you should have started the sentence in a completely different way to articulate the same sentiment).<p>Given there aren&#x27;t many people in general that attain a high level (Novel Authors, Great Lecturers, Debaters, etc.) of linguistic competency, still the few that do attain this, seem to almost always be monolingual or do whatever they are best at in only one language.<p>For me, with one side of my family everything is german&#x2F;polish, with another english&#x2F;spanish, and its very easy to casually speak in whatever language for daily tasks because if you are with family you can just use whichever word comes to mind regardless of what language it is in, and if not the vocab is so common and easy there is no difficulty just saying everything in the one language (even though your grammar is at times influenced by your other languages like copperx says - ahh). But once you go to writing an essay, giving a lecture or presentation, especially in one of the languages you don&#x27;t usually do that in - you immediately realize how segmented your vocabulary is (or at least that happens to me :).<p>Not to mention that in informal settings with family, you are constantly mixing stuff up because your mother in law is speaking polish your wife is answering in german and you&#x27;re asking you&#x27;re wife something in spanish.