Disabling polylang breaks my site

First thing I noticed but I’m not 100% sure if it is caused by your plugin is my images were not appearing on my site and when I went to media library I just saw grey squares instead of the images. Second thing I noticed is my site was not secure when I wasn’t logged in on my site. Trying to find what is wrong with my site I tried disabling your plugin. After I disabled it I got a critical error on my site. Here is the error report:
Gre?ka vrste E_ERROR je prouzro?ena u retku 9 datoteke /home/klikagen/zelenika.klik-agency.com/wp-content/themes/hueman-child-master/functions.php. Poruka gre?ke: Uncaught Error: Call to undefined function pll_register_string() in /home/klikagen/zelenika.klik-agency.com/wp-content/themes/hueman-child-master/functions.php:9
Stack trace:
#0 /home/klikagen/zelenika.klik-agency.com/wp-settings.php(525): include()
#1 /home/klikagen/zelenika.klik-agency.com/wp-config.php(89): require_once(‘/home/klikagen/…’)
#2 /home/klikagen/zelenika.klik-agency.com/wp-load.php(37): require_once(‘/home/klikagen/…’)
#3 /home/klikagen/zelenika.klik-agency.com/wp-admin/admin.php(34): require_once(‘/home/klikagen/…’)
#4 /home/klikagen/zelenika.klik-agency.com/wp-admin/plugins.php(10): require_once(‘/home/klikagen/…’)
#5 {main}
thrown

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