Some users want to completely disable the new option available to users to pick their language & theme at the WorldClient login.
This is an easy one, add either or both of these items into the [Default:Settings] section of \MDaemon\WorldClient\domains.ini:
HideLoginLanguage=Yes
HideLoginTheme=Yes
Note that users can still change their language and theme from within WorldClient’s option page as was possible prior to MDaemon 10.