Where in the registry is the language setting for each user stored?

A. The ID for the current language is stored in the registry value HKEY_CURRENT_USERControl PanelDesktopMultiUILanguageId. When you request a change to the language, the ID for the new language is stored in HKEY_CURRENT_USERControl PanelDesktopMUILanguagePending and takes effect at the next logon. Both registry values store a number that corresponds to the language ID you've chosen. The table below lists the available value.

If you request a language change, then want to cancel the change, you can open a registry editor and change the MUILanguagePending value to that of the MultiLanguageId value.