> Is happens on the console and X. It's not specific to one shell
> (/bin/sh as well as /usr/local/bin/tcsh don't display them).
 
 Console and X differ. xterm is not vt100 console device. And your issue
_is_ shell and console/xterm specific.

> What can I do now to make them usable during normal operation (e.g.
> when hitting Umlauts when sh/tcsh is running, with vi, ...)?

 /bin/sh is not 8Bit-able. tcsh is, but I never really bothered to
use Umlauts in the shell. Is there any reason to do so? Other than
beeing able to type filenames with Umlauts (yucc :-) ?

 As for vi: Never bothered myself as well. vi grokes Umlauts but
displays them in escape code sequences. The file itself contains 
Umlauts as supposed to be.

 Maybe I am too long a UNIX user to change this behaviour :-)

-- 
Markus Illenseer
NetBSD 1.3.2 CD-ROM "Gateway! Vol. 3" now shipping!  See:  http://core.de/