Hi folks
Sometimes I've found a bit irritating when Windows re-sets some language options -- seemingly by itself.

You need to disable Sync across devices - can be done globally or individually -- otherwise depending on other computers / phones / how an Ms account / one drive set up things like themes and language preferences can be spread accross devices -- fine for some - but if you are testing machines for different charcteristics and have a few machines in various states of testing then this can be a real pain.

Here's the google link of what to do if you want to switch sync off. I'm sure there's something in the tutorials too so just a reminder here if you need a quick solution.

How to Disable and Remove Windows 10 Account Sync Settings