I had the same question but with French being the default on Windows 10 rather than the one I wanted so I ended up here.
HoD is very close. I was able to use his suggestion to find the solution for me. This solution uses your current display and input language to change the Welcome screen and possible for new user accounts if you want. So make sure you have the display and input settings while logged in that you want to apply to the login screen before doing the steps:
Click the language on the Taskbar.
Then click Language preferences.
At the bottom under "Related settings," click "additional date, time, & regional settings" which opens the control panel
Click the "Region" option
Then go to the far right tab "Administrative". (HoD's step 2)
In the "Welcome screen and new user accounts" click copy settings. (HoD's step 3)
Tick "Welcome screen and system accounts" (and "new user accounts" if you want it to be applied to those as well). (HoD's step 4)
Click Ok. (HoD's step 5)
I was able to use HoD's suggestion to find the solution here. It's for Windows 8.1, but works on 10 so far.
Hope it will help you, too!
