The keyboard hook is low-level. I don't think even in US layout the hook returns US characters. It returns key codes, they are language-independent. By the way, for the hook function is would not make sense, because current keyboard layout / input language is not system-wide, it's set individually for every different application, which if above the level of the hook.
If you're at the point you may need the current keyboard layout you can always retrieve it.
You can get current keyboard layout for a current thread using this API: http://msdn.microsoft.com/en-us/library/ms646296(v=vs.85).aspx