Thanks for linking the interesting article. Interesting, but I'm not sure about its conclusions based on my personal observations on the subject.
I speak four languages: English, French, Spanish and Russian, none of which I studied, but just, somehow, picked up. Spanish and Russian were my first languages. My parents were Russian and we lived in Mexico so I was immersed in both. I picked up English when we moved to the States; I was about 12. Other than ordinary "English" classes in public school, etc. I never studied the language per se. I was given a trip to France as a High School graduation present. When I arrived in France I couldn't count to three in the language. But then I met a girl. She spoke no English whatsoever, so I learned French on the pillow, as the French would say. My current wife of 54 years is French and perfectly bilingual with English. At home we sometimes speak French, other times English, but it has become so automatic that I would be unable to tell you why we break into one language rather than the other, at times it has to do with the subject being discussed, at other times I really don't know. As for having different cognitive skills and/or different manifestations of personality in one language or another I would be unable to say. My father spoke 8 languages, so perhaps genetics enters the picture, but who knows?
I only wish I could pick up Affinity as easily.