Did you try some other i18n keyboard layouts, like Norwegian or Swedish?

Mine is Swedish, and I am unable to reproduce it.

It crashes with Swedish layout on 10.8.2 when I type Ctrl + ¨ on my computer. (Alt+~+space seems to work, though)

Doesn't crash my Terminal.app. I use a swedish keyboard. Perhaps you could create a new clean account on your computer and try it there? You can always delete the account afterwards.

Interesting. Must be some kind of pref setting or something that's surfacing the bug. Ugh, sounds hard to track down.

Yup, and that's why I suggests you create a new fresh user and try it there. If the bug doesn't show there it's something in your personal settings somewhere, if not it's in the system settings.