foreign languages in dreams

i have a largly multilingual familly. my father is from france my mom speaks french fluently and my brothers and i were raised with english as our first language and french as our second. i can understand everything in french and speak it well but with many gramatical errors. in some of my dreams ill have my dad speak in perfect grammatically correct french and ill answer in english. also my brother spent a year in argentina and he ssaid he even started to think in spanish. so my question is at what point does the brain introduce a new language into dreams and thoughts. why can i create grammatically correct french in my dream but only when my dad is speaking. is it different when the language is learned early. any thoughts would be cool. iv just always wondered about this - thanks

No scientific answer, just a data point.

When my older sister was studying German in Germany, she said she really knew she had “gotten it” when she started dreaming in German. I always thought that was very interesting. She was 18 or so at the time, but had spoken German as a second language since early childhood.

I dream in Cantonese sometimes. Thing is, my Cantonese is really quite limited, but in my dreams I’m totally fluent.

To me it’s more of a mood thing. People code-switch between languages in real life based on how they feel about a situation (or if they want to identify themselves as distinct from those around them, kind of like slang). I think it’s the same in dreams.

If a Thai person on the street comes up to me in a dream, asking directions, I assume he is speaking good Thai, and I somehow understand. He wants me to know he is Thai and is not familiar with how to get to the post office.

When I was taxi-driving, I dreamt of a Russian woman from Ukraine, telling me a very long, sad story about her life, and I thought I understood it fairly well. (Her husband had beat her.)

Once, when I was pissed off at my girlfriend in a dream, I let her know in Spanish, so she would clearly understand the nature of the problem. She responded in English.

At any point. I’ve dreamt that I spoke and understood fluent Italian, a language I have never studied in my life. It seemed real at the time.

On the other hand, I do speak German and French as second languages. I started dreaming in German a couple years after learning it, but I didn’t have my first dream in French until maybe fifteen years after I started learning it.