Defaults to False - per default only English and German are shown in the language dropdown (User > Edit profile > Language)
Changing this global setting requires an additional activation of pending changes
When changed from True to False, the UI default and user specific languages are checked and set to English if a community translation was in place. Any such reset to English is logged as a warning to the details column on the "Activate pending changes" page.
When updating from an older version without this global setting, the UI default and user specific languages are checked and if a community translation was in place this global setting is changed to True to keep the previous language configuration.