I am an ESL (English as a Second Language) teacher with over 30 years experience. Melania Trump read that speech beautifully. Her pronunciation was very good. The only mistake she made was mispronouncing the word “trivial.” It would also have helped if she had delivered the speech using a teleprompter, rather than looking down to read from written pages.
It is very common to never lose your native accent when you move to another country as an adult, even after 30 years like Melania. By that stage in life, speech patterns are already deeply established, which makes them much harder to change. Children, on the other hand, have very few difficulties adapting. They pick up accents easily because they are still developing all their language skills.
@Anonanonanonagain
You mentioned that her speech “was dreadfully read,” which is an awkward use of an adverb. Surely you mean, “It was read dreadfully” a more natural way of saying the same thing.