I don’t know but my limited personal experience has been totally different. Not only learn my children their primary languages faster, they also learn other languages more quickly. I don’t know if that affects their IQ but I don’t see math or science as a much different language.
Of course, speaking a language is only part of the bigger puzzle: staying curious and immersing yourself in the cultures and thoughts of people from diverse backgrounds is IMO even more important and beneficial. While translation is excellent and very convenient today due to the globalization, I’d say it's very hard to understand the people of a particular culture if you don’t understand what they natively and rawly say on various social media platforms. Mainstream media and news paper don’t necessarily reflect these sentiments and predispositions. In fact, they may even hide these “small voices” very well. So, there are clear benefits to using many languages.
Of course, speaking a language is only part of the bigger puzzle: staying curious and immersing yourself in the cultures and thoughts of people from diverse backgrounds is IMO even more important and beneficial. While translation is excellent and very convenient today due to the globalization, I’d say it's very hard to understand the people of a particular culture if you don’t understand what they natively and rawly say on various social media platforms. Mainstream media and news paper don’t necessarily reflect these sentiments and predispositions. In fact, they may even hide these “small voices” very well. So, there are clear benefits to using many languages.