Language is a funny thing. I have friends who have been in America for their entire adult lives and now, in their 60s and 70s, still haven’t ditched their accents — especially the German accent seems so hard to get past; other friends are here for less than a decade and speak flawlessly. Also a degree of physical structure by race, including English speakers in other languages, seems to accompany intonation and accent.
So, degrees and types of fluency vary greatly with individuals and their backgrounds. Being a writer in English of course makes me more fluent in writing than in speaking in all my languages, and I’m able to translate and edit in one or two others in which I would have difficulty holding any but the most superficial conversation. Some people may have a musical ear and “get” accents perfectly without deep understanding. It’s a gift to have a wide range of capabilities. Melania is a Taurus; they are known for tenacity, and dropping an accent may be low on her spectrum of communications priorities.
When an accent carries a stigma, there’s impetus to lose it. When an accent has a certain amount of cachet, there isn’t.
I dont’ have an issue with her accent... it’s her mistakes/syntax in english that are puzzling. My parents have very thick accents, but speak perfect english grammatically speaking. That’s why I’m less likely to believe she “speaks” all of these other languages. I am bilingual, German and English...but can also read french easily. I would never state that I speak french, but I can communicate in french enough that they understand me.