"linguistic" relates to languages.
i would think a linguistic savant is anyone with an extraordinary ability to acquire new languages with ease, especially in adulthood where the brain is usually less plastic than in childhood and learning new languages becomes more difficult.
i'm not sure if it's synonymous with "polyglot", that term might simply mean anyone who can speak many languages, not saying anything about how easily they acquired them.
_________________
הייתי צוללת עכשיו למים
הכי, הכי עמוקים
לא לשמוע כלום
לא לדעת כלום
וזה הכל אהובי, זה הכל.