After upgrade from Zabbix 3.2.9 to 3.4.4 using yum update(via rpm) i'm can't change frontend interface language to Russian(in my case).
Steps to reproduce:
Change interface language for Russian in my profile and click "Update" button.

Result:
But interface language not change.
Expected:
In rpm package zabbix-web-3.4.4-1.el7.noarch.rpm no files for locales:
rpm -qlp zabbix-web-3.4.4-1.el7.noarch.rpm|grep locale/ru
/usr/share/zabbix/locale/ru
/usr/share/zabbix/locale/ru/LC_MESSAGES - empty
But in 3.4.3 version files available:
rpm -qlp zabbix-web-3.4.3-1.el7.noarch.rpm|grep locale/ru
/usr/share/zabbix/locale/ru
/usr/share/zabbix/locale/ru/LC_MESSAGES
/usr/share/zabbix/locale/ru/LC_MESSAGES/frontend.mo
For temporarily solution i'm manual copy frontend.mo file for my russian locale to /usr/share/zabbix/locale/ru/LC_MESSAGES.