When thinking about this question I asked, I wondered: Is there really no way of finding out if a adopted SD is present?
With a Motorola G3 there were two paths returned by getExternalFilesDirs() when an external SD was present, but only one (the emulated one, thats always present) when formatting the SD as internal. Other devices seem to behave similar.
So, if I am looking to know if there is a internal SD present, where would I need to look? Is there anything (non manufacturer specific) provided, so e.g. I could check, if the user expects to use the internal emulated Environment.getExternalStorageDirectory() because he has mounted a internal SD?