[bite_your_idols]

It's not an addon bug, it's one of the two:

1. you have chosen Manual Selection in InputStream.Adaptive settings
   
2. you didn't properly configure Kodi. Settings > Player > Language, more info here. The link is specific to subtitles but in the same place you also find audio language settings.
   

Inputstream is set to auto.
In kodi>settings> language>preferred audio language I always use "original language" so I get the original one no matter what it is: english, french, spanish... If I do so, amazon addon always starts in german (audio track #1).
If I change that setting to "content prefefined" ( maybe title is not this one exactly because my UI is in spanish), the addon behaves the same.
If I change that setting to a defined language, e.g. english, addon starts in that language but this is not a useful solution because if it is a french movie it will use english audio, the same as if it is a spanish one... I don't know if I explained myself properly, or maybe I am missing another setting.

Thanks!