"Japan and China are countries in Asia."
Translation:Japanio kaj Ĉinio estas landoj en Azio.
I don't speak Vietnamese myself, but I tried to listen to the Vietnamese pronunciation of the name of the country [linked from the English Wikipedia; very low sound] page, and it seems to be closer to "vjet-" than "viet-" (i.e. not "vi-et-").
Not all countries have an Esperanto name "close to the country's pronunciation", but some have.
In this case I suspect it's more due to a "one syllable, instead of two" reason, though.