@jengelh said in Debian Stretch: kopano-monitor not starting, "unable to initialize locale":
error message was “unable to initialize locale”. this happend on a system with non en_US locale.
You should make sure the locale is actually installed before trying to make use of it.
Good point @jengelh , on Debian this is normaly already installed, then its only enabling it.
run : dpkg-reconfigure -plow locales select the needed locales and restart the kopano service.