Traslation work only in frontend, backend always in english...

I have a trouble with traslation. It is visibile in frontend (italian) but is no visible in backend that is in english. My site is monolanguage in italian. I update Joomla from 3.9.2 to latest 3.9.14 and JEvents to latest version 3.4.50. Problem is only in online version of site. In localhost with XAMPP 7.2 all work fine. I try also production DB dump to localhost, localhost show correctly italian in backend, production no.

Where I can investigate?

Thank you in advance for reply,
FF

PHP Version : 7.2.22

MySQL Version : 5.5.62-38.14-log

Server Information : Linux webxc294s06.ad.mysite.it 3.10.0-862.2.3.el7.x86_64 #1 SMP Wed May 9 18:05:47 UTC 2018 x86_64

Fix jQuery? : Yes

Load JEvents Bootstrap CSS? : Yes

Max Input Vars ? : 1000

Club code set? : No  

User Agent : Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:72.0) Gecko/20100101 Firefox/72.0  

Joomla : 3.9.14

component_com_jevents : 3.4.50

component_com_jce : 2.6.26

module_mod_jevents_cal : 3.4.50

module_mod_jevents_custom : 3.4.50

module_mod_jevents_filter : 3.4.50

module_mod_jevents_latest : 3.4.50

module_mod_jevents_legend : 3.4.50

module_mod_jevents_switchview : 3.4.50

plugin_content_jevents : 3.4.50

plugin_finder_jevents : 3.4.50

plugin_installer_jeventsinstaller : 3.4.50

plugin_search_eventsearch : 3.4.50

plugin_system_gwejson : 3.4.50