You may experience problems reading the new jLog xml-based configuration files. E.g. SuSE V 9 or newer uses UTF-8 as the default Character Set. The Character Set should be changed to e.g. ISO-8859-1 as follows:
In /etc/profile (or the profile for the current user only):
LANG=en_EN.ISO8859-1; export LANG
MM_CHARSET=ISO-8859-1; export MM_CHARSET
In /etc/csh.login (or the login file for the current user):
setenv LANG en_EN.ISO8859-1
setenv MM_CHARSET ISO-8859-1
In a dedicated script starting jLog:
xterm -fn 9x15 -geometry 80x15 -e jlog
More from W3C on Internationalization (Country codes, etc.).
Thanks to Christian (DF5OP) for helping me with these issues!