Today, I also faced same issue when I upgraded the plugin All In One WordPress Security.
The error is something like below,
[Tue Jul 10 12:37:42.727556 2018] [:error] [pid 2237] [client x.x.xx.x:25795] PHP Fatal error: Call to undefined function switch_to_locale() in /data/htdocs/example.com/wp-content/plugins/all-in-one-wp-security-and-firewall/other-includes/wp-security-rename-login-feature.php on line 443, referer: http://www.example.com/wp-admin/update.php?action=install-plugin&plugin=all-in-one-wp-security-and-firewall&_wpnonce=7ccaa5d7fd
I disabled it and it was back again. I think the issue is with the WordPress core, I am using WordPress 4.4.16. And switch_to_locale() is introduced in 4.7.0
Thanks
