Error 504 - localization issue?

Hello, could you please help me? I installed Commerce Kickstart 2 and after adding several other modules, a 504 error started appearing, but only on the administrative pages and specifically when navigating to /admin/config.

Knowing from your previous responses that this is an Apache issue, I contacted my hosting support. They asked me for the login and password to access the site.

After some time, they wrote: "This problem is caused by the current localization, which is likely done incorrectly. The localization is now switched to English; please check the functionality of your site."

Now the site indeed opens on those pages, but everything is in English. Could you please advise if I can somehow control this process? Maybe I can bookmark the localization and disable Russian if it starts happening again?