Regarding SIM -
Sorry @ThelmaLou, the SIM is largely just a key to your carrier’s network, it doesn’t really store any settings or information (outside of very, very limited contact storage if set up that way).
I suspect @gnoitall is correct, it hasn’t completed the setup yet, and therefore isn’t changing the language settings. This site should be helpful
It’s a step by step ‘on-screen’ guide to the language set up for the device.
When I get to the page that matched the one you linked prior, it indicated you had to grab the ‘hamburger’ (three stacked lines) to the TOP of the language list to set as the default, then press the home screen to return. Hope this is a fix.
It’s enough for now.
Must drink alcohol for a little while…
Happy to help. I do a lot of in-person and remote Android support covering a lot of devices and a lot of versions of Android, so (like the insurance commercial goes) I’ve seen a lot.
I still recommend removing any languages from the device you don’t plan on purposefully using. Otherwise they may get used when you weren’t planning on it.
As to the rest of the international-ness, I don’t know enough about the specific device to guess. Stuff like available radio bands (compatibility with phone networks) might factor into it, for instance. Slot your SIM and see if it works or if the phone rejects it.
And I heartily endorse the glass of wine and a few minutes of relaxation at least. Savor the victory and gather your resolve for the next battle. 
I will do that… maybe tomorrow. A million thanks.