This removes the (usually) EN button from the top left corner of your logon screen. It also removes the mysterious extra language from your language toolbar especially if using non en-US as your default language.
First, navigate your way to the Control Panel.
If you are using the Category view click on the link Change keyboard or other input methods under Clock, Language, and Region.
If however you are using one of the Icon views click on the Region And Language link.
On the Region and Language window, click on the Administrative tab. See image below.
Then in the Welcome screen and new users accounts box, click on the Copy settings… button (Admin privileges may be needed). See image below.
Next, in the Welcome screen and new users accounts settings window, under the heading Copy your current setting to: Check the boxes against Welcome screen and system accounts and New user accounts (This covers all options!). See image below.
Finally, OK your way out.
Re-booting may be required before you will see any changes.