Hello,
the null is supposed to be the default language of sogo. Do you have in your sogo.conf SOGoLanguage set?

the sogo.conf contains
SOGoLanguage = German;

Could you try to remove sogo and reinstall it? Do a backup of your sogo.conf just in case.

And if it doesn't work can you provide more logs? (You may need to compress the file in order to attach here)

after
yum remove sogo
yum remove sope

yum install sogo sogo-activesync sogo-debuginfo sogo-devel sogo-ealarms-notify sogo-slapd-sockd sogo-tool sope49-cards sope49-cards-devel sope49-core sope49-gdl1-postgresql sope49-ldap

and using the old sogo.conf i'm not able to start sogod again.

I've seen a message due to gnustep and reinstalled it also

And systemctl start sogod tries to start it and i see with top

sogod -WOWorkersCount 40 -WOPidFile /var/run/sogo/sogo.pid -WOLogFile /var/log/sogo/sogo.log

is working with 100% CPU but no log entry or hint

systemd[1]: sogod.service start operation timed out. Terminating.
systemd[1]: Failed to start SOGo is a groupware server.

-- Subject: Unit sogod.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit sogod.service has failed.
--
-- The result is failed.

Now the sogod is running again. I had to switch the userid and groupid for the sogo user from the new created values to the values used before.