I have a friend who studied French and Spanish at the same time, using the same method I described in my story. We wondered if doing two languages at the same time would work. He tried it essentially out of curiosity.

And he did really well!

We found out later that neurologists think that the brain carves out language spaces, actual physical networks of neurons, for each language.

Most people learning their first non-natal language have two spaces. One for their original language, and one for everything else.

Eventually, though, with enough study, each language gets its own space — which is why people aren’t as likely to mix vocabularies up as you’d think they’d be.

Once your brain hits the “Portuguese” switch, that network dominates.

Or at least that’s the theory! I find some truth to it.