Steps to reproduce:

1. Changes in configuration...ihad been trying change the language to spanish
2. Navigate to screen title...Language GUI
3. Click on screen element...Administration > General> GUI
4. ... I was checking this document https://www.zabbix.com/documentation/6.0/en/manual/appendix/install/locales?hl=languages but The change of language is not working as well.

Result:
See screenshot. 2022-05-28 00_02_48 where the language on System Locale is es-ES and the screenshot 2022-05-28 00_02_30 where you can see the packet of language is correct.  But the system language GUI doesn't show the Spanish language: 2022-05-27 23_59_09 screenshot

Expected:
This documentation https://www.zabbix.com/documentation/6.0/en/manual/appendix/install/locales?hl=languages should work although of that my implementation is on Zabbix appliance model on HyperV with centos 8 and ngnix.