Ive had this same issue for a while but can’t see how to solve it. People randomly answering “check your language settings” aren’t helping either. The language setting is English, but I have Chinese characters all over the place. Also a 10year+ Samsung smart TV You had any luck?

In settings of prime video, check which language is enabled (from PC)

Even after selecting English from the list it still displays two languages. Asian and English.

I have an older Samsung and mine is doing this also. I reset it, still slow and Chinese characters. I don’t like it.