Working for the World Bank during the 90s, I travelled to Vietnam on several occasions in 1995 in connection with preparing a primary education project. This was actually the first World Bank project to be prepared (and later implemented) in Vietnam after the Vietnam War (United States only at that time "allowed" development cooperation activities to go ahead.)
Being a social scientist with a strong interest in indigenous peopls / ethnic minorities, I was working specifically on a project component that aimed at providing bilingual language training to children in the many ethnic minority groups, sometimes refered to collectively as "Montagnard(s)", that live in the mountain areas (the term "indigenous" is not allowed used in Vietnam). These children have to learn Vietnamese in school, and in this project component I, together with my counterpart in the Ministry of Education, acordingly focused on organizing training in the vernacular languages (of which there are about as many as there are ethnic groups, more than 50).
A video (see Sources) presents three types of bilingual brains and shows how knowing more than one language keeps your brain healthy, complex and actively engaged. Fascinating! In theory, then, Montagnard children who may have benefited from this World Bank project, should have an advantage of lowland ethnic Vietnamese children!
Reading this article, however, I started wondering what became of this project? Put differently, did it make an impact? Is bilingual training for Montagnards going strong today, 25 years later? I admit I have an inkling that this may not quite be the case...
Nacamulli, Mia. nd. "The benefits of a Bilingual Brain", at: https://www.ted.com/talks/mia_nacamulli_the_benefits_of_a_bilingual_brain?