I don't see the information on this study that says foreign language improves global competence but I think perhaps it is the interaction with the native speaker from another country that causes the improvement in global competence. It is time to start studying global collaborative projects and their impact on global competence. Another point is that this article says that "it has been proven that proficiency in speaking a second language increases overall academic achievement."
Unfortunately this author has no citations or links to follow and learn about. Perhaps it is citing the original NEA article. I just think this author can do better although I'm intrigued by what it says.
"According to a study by the National Education Association (NEA) in 2010, global competence stems from proficiency in a foreign language."