http://mappingignorance.org/2014/02/03/mandela-was-right-the-foreign-language-effect/
Summary: Across the board, people are less prone to cognitive bias in a non-native language.
Conclusion: If all important discourse was conducted in Latin, or any other language native to no one, people would make better decisions.
Corollary: All the attempts to make a constructed "scientific language" actually could have worked relatively well, for reasons entirely unconnected to the painstaking scientific structure of the languages.
I don't know, but given that we're comparing between one of the poorest regions of the world and one of the richest, I'd expect controlling for all the confounders to be a nightmare. No one's claiming this to be the sole determinant of rationality, after all, much less peaceableness.