In Windows 10 release 1803 Microsoft have managed to create a new bug whereby on some localised (i.e. non US English ) computers, you suddenly fiind US English has been installed and is non-removable using the new Languages Settings applet.

The solution to this is to run some PowerShell commands, as below:-

First, get the list of languages you have installed using:

Get-WinUserLanguageList

You'll probably find you have your main language *and* English US installed. To get rid of US English, you have to run the following slightly confusing commands to "install" and then set as default, your desired language. So, to set UK English as the default and ONLY language, run the following:

$1 = New-WinUserLanguageList en-GB
Set-WinUserLanguageList $1

Having done that, you'll see that US English has magically disappeared :-)