This isn't really a bug as the behavior is expected just need to see the logic behind it.
The behavior of the Language selection is the same as earlier version for 7.4x. The result of an apply in the language change is to write the current value to the webadmin httpd config and then restart webadmin. Webadmin then loads a new connection and checks its config file which returns the configured language.
So if I change my language to English that value is now written to the file only when the Apply is hit.
