I use Microsoft IME for Japanese language input but "ALT + '" does not toggle between alpha and hiragana! I thought that this might be because I have set my IME key settings to "ATOK" key settings (in IME properties, "Editing Controls" tab - translated back from the Japanese since my system is Japanese) since I was used to using ATOK prior to the release of IME.
However, returning my IME key settings to "IME" settings. None of keys in any of "Microsoft IME" "IME standard" "VJE" "WX" or "ATOK" (the complete list of possible ket settings, seems to include the "ALT + '" on my machine.
However, in any event fine grained key settings are possible in this same tab, so anyone who has problems with IME shortcut keys being duplicated in an app can change their IME key settings to whatever they like. I would have posted an image but I lack the reputation.