I thought I'd switch to zsh, so I did just that with
chsh -s /usr/bin/zsh user, unfortunately, it broke my compose key (unresponsive both in the console and in an X terminal); also, when I read email in emacs rmail, Swedish characters are not displayed correctly (diamonds in the console, question marks in an X terminal) - but it is possible to display them, for example if I
cat the mail files instead.
To possibly reinitialize the compose key, I run
setupcon again as superuser but it didn't help. In
/etc/default/keyboard, this line is present
As for the compose key in X, and the character set in both the console and an X terminal, I'm clueless because I can't remember anytime "setting up" those things, they just worked.
To double check, I switched back to bash with
chsh -s /bin/bash user, and everything worked as before. I examined
.bashrc to see if I possibly had done some keyboard/charmap initialization there, but I couldn't find anything to that extent.
zsh --version zsh 4.3.17 (i686-pc-linux-gnu)