[leidenfrost]

I wonder if these studies also take in account indigenous languages and its native speakers.

People from Paraguay speak both Spanish and Guarani. A lot of people from Mexico speak both Spanish and Mayan.

Does that have the same effect as the son of a family that speaks English and German?

[keiferski]

In terms of the knowledge sense I mean, I think it is logical that the more distant the worldviews of the languages, the greater the effect. Even more so if they both have a large media / cultural sphere.

[FlyingSnake]

I think so, yes. My daughter speaks English and German fluently and I can see she has deep insights into these cultures. (She also speaks 2 other languages)

She once told me that she likes to read conversational books like “Greg’s Tagebuch” in German while “Harry Potter” type books in English.

[bogdan]

Could it also be because translations are never as good as the originals? One thing that comes to mind is translated songs, they usually sound off and forced to my ear. On the other hand I never read the same material in two languages so it's hard to really have an opinion but I did CS in another language than English and can say very confidently say that it was a huge pain to discuss with professors CS terms that were force translated into my native tongue, it was unnecessary and even though it's been many years since I graduated I still have those terms imprinted into my mind.