Windows 10 1803, Delete language greyed out

Start PowerShell as admin
You can view your language list with Get-WinUserLanguageList
$1 = New-WinUserLanguageList Enter
fr-CH (choose the language you want) Enter
Set-WinUserLanguageList $1 Enter

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

After rebooting everything work fine