You use logic. In the west the child learns writing and reading in preschool. It learns all it needs when it is 6 years old. For Japan learning 2132 compulsory Kanji lasts until the end of high school. That's 16 years old."Fact"? where do you find this fact?
for example, many people say French language is difficult to learn than English. But French wont change their language. They are proud that they have so many famous novel who wroten in French.
For Vietnam case, why is it reasonable to change Vietnam's tradition writing system?
I'm NOT saying vietnamese should use chinese characters. Instead, they should keep their tradition.
I'm not saying vietnamese did specially, because chinese did the same thing too . In 1950's, chinese simplified the writing system and invented simplified chinese.
In my understanding, that's wrong.
Let's use my experience in learning foreign writing systems. Let's compare Latin with Cyrillic, since it's also an alphabetic writing system. It has 33 letters and it didn't take one week to memorize them all. Japanese I've been learning for 3 years and I still need dictionary help very often. Not to understand what's written, but how to even pronunce it.
Vietnamese can do what they want. Why are you even comparing languages to writing systems? Do you know that English was originally written in Germanic runes? If English adopted latin, then what's wrong with Vietnamese changing it?