Changing the Region changes the Language on iOS11? I'm really confused about changing Language verse Region on an iPhone running iOS11.

Apple discusses here about changing the Language and the Region:


  "For iOS, changing the language restarts Springboard and quits running
  apps. So the next time you launch an iOS app, it uses the new language
  setting. ... For iOS and Mac, the region and calendar settings can be
  changed at any time, even when your app is running."


So, I take that to mean that if I change the Language, the App will have to be restarted.  But, if I change the Region, the App will not have to be restarted.  I've been chasing my tail for an hour or more wondering why my App was shutting down when I was just changing the Region.  Then I read the text on the screens, below, a bit closer.

My iPhone is running English (U.S.).  I go to Settings>General>Language &amp; Region.  This is what I see:



I go to the Region button and I click it. And it shows me a long list of countries.  Here's what I see (note it says Region at the top of this list):



I click United Kingdom and then Done at the top right.  Then I see this:



It is giving me the choice to confirm my selection of English (U.K.) or to stay with English (U.S.).  But note also that it says:


  "Would you like to change the iPhone language to English (U.K.)?"


So, here's my confusion. Why am I being asked to change the Language at this point when I'm clearly choosing a Region? What am I missing here?

rmaddy made a comment in response to the above:


  You are being asked if you want to update the language in addition to
  the region change. This is because your current language is US English
  and you are now choosing a region which generally speaks UK English.
  So iOS is being helpful and offering you the additional option of
  changing the language that best suits your new region. If you choose
  the "Keep ..." option then only the region is updated and not the
  language.


That made a lot of sense and I thought it was the answer but I'm noting that all of the following scenarios (some of which only seem to be changing the Region) still result in my App shutting down and I am having trouble reconciling that fact with the documentation which says:


  For iOS and Mac, the region and calendar settings can be changed at
  any time, even when your app is running.


Scenarios which result in my App shutting down:


I change Region from United States to United Kingdom, click Done and
then choose "Change to English (U.K.).  As per rmaddy's comment, I
think this changes both the Language and the Region.  App shuts
down.
I change Region from United States to United Kingdom, click Done and
then choose "Keep English (U.S.).  I think this changes just the
Region to U.K. but leaves the Language as U.S.  App shuts down.
I change Region from United States to U.S. Virgin Islands, click
Done and then Choose Continue when it says, "Would you like to
change the region to U.S. Virgin Islands."  App shuts down.


Please note that the app which is shutting down is one I am developing. Written in Objective-C for iPhones and iPads for iOS9 and up.
You are being asked if you want to update the language in addition to the region change. This is because your current language is US English and you are now choosing a region which generally speaks UK English. So iOS is being helpful and offering you the additional option of changing the language that best suits your new region. If you choose the "Keep ..." option then only the region is updated and not the language.