Search notes:

Registry: HKEY_CURRENT_USER\Keyboard Layout\Preload

The values under HKEY_CURRENT_USER\Keyboard Layout\Preload seem to represent the keyboard layouts a user can choose from on the taskbar (see quick language list). These values are the hexadecimal representation of a language id.
A more humanly readable for form of these ids is found in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout\DosKeybCodes. (For example 807 for Swiss German (sg) or 409 for United States (us)).
The value whose name is 1 seems to be the default keyboard layout.

Misc

The PowerShell cmdlet get-winUserLanguageList.

See also

The value of Preload under the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\IniFileMapping\KeyboardLayout.ini.
The value of Languagues under the registry key HKEY_CURRENT_USER\Control Panel\International\User Profile

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