How do I know which keyboard locale file I'm using for my keyboard layout?
It's determined by the list in the "Language &amp; Text" preference pane's Language tab.



The plist file that is chosen is the one that matches with the language in the list that is highest to the top that has a match.

For example: if your list shows "Canadian English, UK English, Spanish, …", Keyboard-en_CA.plist will be chosen, as it best matches Canadian English. If the list is "Português, Suomi, English, …", Keyboard-en.plist will be chosen, as it best matches English, which is the language closest to the top that is available. (The last is assuming that Portuguese and Finnish plists aren't available.) If there are no languages in the list that have plists present, the Keyboard_default.plist would likely be chosen.