Ever time I watch a show on my new Google TV chromecast with Amazon Prime Video it always wants to do incidental subtitles in Danish (I think it's danish). Not subtitles all the time, but when important stuff like text on video images or whispering segments that would normally get subtitled without closed captioning. And if I turn on CC it is danish all the time. I can change it in the video player options, but it only lasts through the current viewing session.
Is there some weird setting I don't know about that has me pranked into danish as a default language? On the amazon website? in the app? on my chromecast?
Maybe check your subtitle settings on your amazon account, on their website.