Localized version offers upgrade to en-us version

(Answering my own question)

It is now 1 week after posting my question. I just revisited the dashboard.
There are now two updates available: WordPress 4.3.1–nl_NL and WordPress 4.3.1–en_US.

So it looks as if the localized update takes some more time to prepare.

I will not click anything right now, assuming that the update will go automatically.

To be continued…

Added: Yes, the automatic update to the Dutch version came through…