I've noticed this with shows that have dialogue in multiple languages. For reference I live in Germany, so on amazon.de there will be shows available in German and "original voice" (usually English), titled
[dt./OV]. This lets me select English as the audio language and "none" as the subtitle language. When I do this I get no subtitles for regular dialogue. However, speaking in foreign languages, e.g. Spanish, will still be subtitled in German, which is very annoying if I'm trying to watch a show as originally intended. Is there any way to convince Amazon's player to give the complete original experience, including no subtitles and English/original for foreign dialogue?
I suspect the answer will be no since I haven't found any hidden settings, but maybe I missed something. My guess is that Amazon supplies subtitles and audio tracks in multiple languages but only the German render of the video and that these foreign language subtitles are baked into that video file. In that case, I would be very disappointed with Amazon for providing supposedly OV content, but not even bothering to switch the video source to the right language!