When I visit your site and set it to Windows-1251, I get a blank page and these errors (same as the other sites).
I’ve just heard an update from the user though — they are using Windows XP with Chrome 49, so that is probably the source of the problem.
I did a quick search through the analytics and there have been 281 visits by 85 users on Windows XP in the past 28 days. I don’t feel like our site needs to support Windows XP, but I’d like to figure out a way to at least serve those people a “please upgrade your browser to use this site” message.
I’m going to recommend that this user upgrades the OS, at least to Linux.