Hello,
This is an issue in the win 10 April update (1803).
I cannot remove input language.
My keyword is bi-lingual - English-US & Hebrew.
I have a third language - English UK, but I cannot remove it.
Windows display language is English UK (its OK, does not matter is its US or UK).
In setting -> Time & Language -> Region & Language
the "Remove" is disabled for both EN-US & EN-UK
Previous major win-10 update (creators) also re-introduce the EN-UK, but it could be removed by the setting.
Windows display Language also cannot be modified (no need to, but its wrong).
My user is an Admin