This is probably the only bit containing a bit of advice expressed in the negative (i.e. 'Don't do . . .). No real reason. I just couldn't think of another way to suggest that you give bilinguals a wide berth.
I’ve nothing against them. I’m bilingual myself, after all. But they often have a funny way of regarding themselves. It’s too easy for them to think of themselves as special, whereas anyone could be in their shoes if they’d been brought up in a bilingual environment as the normal state of affairs.
Being bilingual feels like nothing special, believe me. It’s like you have a sort of extended language, and you simply slide from one side to the other to use them. It’s easier than slipping on a pair of sunglasses.
Such people don’t know how they do what they do. And because of that, they can’t explain to others how to do it. They can’t understand why everyone else does find it as easy as them. They just make you feel dumb when they show off their trick.
A few of us—bilinguals—remember what it was like to assimilate another language. Maybe we did so at a later stage, or, like me, they switched between languages several times. We at least understand what is involved. But even that isn’t sufficient for us to be able to train others. We’re not qualified—not unless we explore the process more deeply.
It’s interesting that bilinguals may face just as much of a hurdle to learn a third language as you do your second.