To be more precise, he learned the northern dialect and accent of the Vietnamese language. You are quite correct, LH, that Vietnam was and is one country, artifically divided as Korea is and Germany was. The US should also be included, I suppose, as we are artifically divided from our Northern states, such as Ontario and Labrador and Alberta. After we reunite with with them we will, of course, have to embark upon a massive campaign to teach our long-separated citizens to speak and spell correctly, of course.

My brother used the example of the P and Q Celtic languages to explain the difference between the dialects of North and South Vietnam and the way he explained it makes sense. You should be able to work it out for yourself from there.