[barry-cotter]

tl:dr It's fluency that impacts utilitarianism, not nativeness.

Being able to communicate in two languages is not the same as being bilingual. The study in question suggests that thinking/communicating in a language that one is less than fluent in leads to more utilitarian decisions.

The important thing here is fluency, not nativeness. I am fluent in German but I started learning it at 12. German is not a native language for me but I am fluent in it. As such the study suggests I should be equally utilitarian in it and English, my mother tongue. But my French and Mandarin are both quite bad so I should be more utilitarian in them because I must be more deliberate.