Search notes:

Registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout\DosKeybCodes

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout\DosKeybCodes lists the installed keyboard layouts.
An eight digit hexadimal value points to a (usually) two character string that represents the layout.
The last four digits of this hexadecimal value apparently correspond to the language id (or standard locale?).
A list of values can be extracted in cmd.exe with 
C:\> reg query "HKLM\SYSTEM\CurrentControlSet\Control\Keyboard Layout\DosKeybCodes" | sort

Thanks

Thanks to spyros 8 who notified me of a typo on this page.

See also

HKEY_CURRENT_USER\Keyboard Layout\Preload shows the preferred keyboard layouts.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\Language

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