Netflix only shows audio/subtitle tracks that are in languages they think are relevant to you.
But nowadays you can configure additional visible languages yourself on the language settings page (checkboxes under "Programmes & Films Languages") without changing the UI language: https://www.netflix.com/LanguagePreferences
Seems silly to me not to list all available languages. I would have never known this if you didn’t tell me. I didn’t slipped my mind to consider its a Profile Settings thing.
But nowadays you can configure additional visible languages yourself on the language settings page (checkboxes under "Programmes & Films Languages") without changing the UI language: https://www.netflix.com/LanguagePreferences