Have you requested Netflix’s permission to translate their movies?
Not sure if the team has a reaction to this, but it is likely a non-issue, AND something that any content creator would likely be happy about. But essentially, the Netflix subtitles (that are provided to the viewer) will be used for both languages, if available. If the translation language’s subtitles are not already available from Netflix, the auto-translation occurs on the fly.
As a side note, the translation services have to be paid for, literally by the word, every time they are shown. I am guessing that this is why the machine translation is not included in the free version of the service.
But if you are running the free version, you are seeing Netflix-provided subtitles in both languages.