Sheesh. For the last, say, eight years I’ve wondered why Japanese keyboards required one to punch both Shift and Caps Lock to turn caps lock on. And now that I’m on mostly English OS’s these days, I think I know: Caps Lock is (was?) an alternative to the henkan key. Probably before there were Japanese keyboards, there was Caps Lock Henkan. And I guess
Alt-` emerged for people who had become accustomed to the having a real henkan key.
Anyway, for anyone else out there suffering through Japanese emails on English windows, here are some useful key combinations:
Alt-Shift: Toggle Input Language
Caps Lock: Henkan (while in Japanese input mode)
And beware of installing both English and Japanese keyboards under the installed default keyboard settings. The keyboard layout will change randomly and drive you bonkers.