Even if bilingualism doesn’t necessarily make you a super-genius, it’s still a good way to, you know, speak two languages.
And combine them! My daughter (who speaks English and Bulgarian) generally sticks with one language or the other depending on who she’s talking to, but if she doesn’t know a word in one language, she’ll substitute the word she knows in the other.
“Gushe me!” from gushkam “to hug”
“That’s not a pacifier! That’s a beebee!” from bibi, short for biberon “a pacifier”
“Leet the ball” from ritam “to kick”
“I’ll get the suppoon” from supon “soap”
“He’s a maister” from maistar “repair-man, contractor”
“I’ll boowa the shoes” from da ubuya “to put on shoes” (complete aspect)
“It’s a pirrin” from piron “a nail.”
But also, see something cool? She doesn’t just use the Bulgarian word in an English sentence. She transforms the word so it matches English phonology and grammar. She stripps off grammatical markers like the definite article in supon-at and the conjugation in rit-am (which is totally ungrammatical in Bulgarian). Then she Great-Vowel-Shifts everything so she pronounces the word with an American accent to match the rest of the sentence. The unstressed u in supon [supo’n] becomes a short “uh” in suppoon [sʌpu:n], while the stressed u in gushkam [gu’ʃ kam] becomes a long “yu” in gushe [gjuʃ]. And this happened even though nobody has ever said “gushe” or “suppoon” to her.
These transformations from Bulgarian to English show that my daughter has internalized the grammar and pronunciation of both languages. From examples like kompyutar/computer and stopvam/stop, she has generated a list of rules she can use to predict what the English version of a Bulgarian word ought to sound like. And she does it so well that, even when she’s wrong, she sounds like she’s right. Doesn’t it make sense to boowa your shoes?
This is creolization, where people (always children) merge the languages of their parents (often through an intermediate pidgin) to create a new language with its own self-consistent rules for using and generating speech. Middle and Modern English probably evolved from a creole of Anglo-Saxon and old Norse in just the same way.
Note I don’t coach her to use the words. In fact, when she does, I correct her with the standard English words, since I want to be able to communicate intelligibly with English speakers. But since it’s been shown that children don’t listen to their parents, I don’t think I’m in any danger of killing this English-Bulgarian Creole.