acutally I got the problem, that on FileVault encrypted Macs the input menu for keyboard layouts won't show up in the boot screen.
The setting for the keyboard input menu is located in /Library/Preferences/com.apple.loginwindow with the key showInputMenu and a boolean value.
If I try to set the value via defaults write, the checkbox in System Preferences is active and the input menu is shown in login window. BUT if the computer is FileVault encrypted, the input menu won't show up in the boot screen.
Only if I set the checkbox manually in System Preferences, the input menu shows up in loginwindow and in boot screen.
I tried Composer to evaluate which files are changed during clicking in System Preferences. The only valuable file is /Library/Preferences/com.apple.loginwindow.
Does anyone have the same problems?
Thanks in advice,