[SlySherZ]

If I remember correctly, when you learn a new language after age 10, the brain encodes the new language in a region adjacent to the one where your mother language is encoded, which means that any localized injury on this part of the brain may impact your ability to speak just one of them.

Source: Sapolsky's lecture about language: https://www.youtube.com/watch?v=SIOQgY1tqrU&list=PL150326949...

If you want to understand better how the brain works, I really recommend watching the whole course.

[temetnosce]

I grew up speaking Mandarin in my household and spoke English at school, but I also picked up Spanish in highschool and Japanese in college.

If I were to guess, my brain would probably place Mandarin and English in "mother language" part of the brain and Japanese and Spanish part in the adjacent region. I wonder what I would lose if I were to sustain an injury. Would I lose one group over another group?

On another note, as with many American highschool students learning Spanish, I fell out of practice and now I can't really communicate in Spanish at all. When I do attempt to speak Spanish, I notice that I sometimes replace words in Spanish with Japanese ones. Can't be sure whether or not it's because of phonological similarities of Japanese and Spanish, or maybe my Japanese overwrote some of my Spanish.