Windows 10 April 2018 Update added an extra Language and I cannot remove it

Finally found a solution using PowerShell.

You can view your language list with Get-WinUserLanguageList

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

now you can check again your new language list with Get-WinUserLanguageList Logoff, Reboot. After rebooting you can add another languages if needed.

Just trying to improve naduvko's answer.

You can directly specify the entire list of languages when running the PowerShell script.

Like this:

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

The first one (en-US in this example) will be the default.

Adjust as needed.

(Yes, it's ridiculous that we need to program PowerShell to modify the fricken input languages)