English locale missing log-specific messages

[Yhor Chelnokov]

Cron job sends these messages to email:

Error: Invalid display - keyword cannot be found: Display line: display --to LOG --type PLAIN --log-indent 2 ROOTKIT_MALWARE_LOGIN_BDOOR_LOG
Error: Invalid display - keyword cannot be found: Display line: display --to LOG --type PLAIN --nl --log-indent 2 ROOTKIT_MALWARE_SUSP_DIR_LOG
Error: Invalid display - keyword cannot be found: Display line: display --to LOG --type PLAIN --nl --log-indent 2 ROOTKIT_MALWARE_SNIFFER_LOG
Error: Invalid display - keyword cannot be found: Display line: display --to LOG --type PLAIN --nl --log-indent 2 ROOTKIT_TROJAN_XINETD_LOG

Reproduction:
sudo rkhunter --cronjob --report-warnings-only --appendlog > /tmp/rkhunter.log
cat /tmp/rkhunter.log

What happened:
Locale file /var/lib/rkhunter/db/i18n/en is missing messages for following "keywords":
ROOTKIT_MALWARE_LOGIN_BDOOR_LOG
ROOTKIT_MALWARE_SUSP_DIR_LOG
ROOTKIT_MALWARE_SNIFFER_LOG
ROOTKIT_TROJAN_XINETD_LOG

Copying these manually from older version fixed the problem.

OS version: Ubuntu 18.04.2 LTS
Package version: 1.4.6-2~ubuntu18.04.1
Expected: silent cron job completion
Got: unclear report about something missing