1- Activated plugin: Fatal error: Call to undefined function is_user_logged_in() in /home/content/20/11289920/html/wp-content/plugins/user-language-switch/user-language-switch.php on line 117
2- I deleted the plugin through ftp, now the front-end and back-end are working again
3- Only when i try to click on the plugin section it still gives "Fatal Error", so what files i need to remove in order to get the "install plugin" section to work again? PS. Like i mentioned in #2; "i removed the plugin manually"
(right after activating i got the error at #1 for the whole site (front-end + back-end) and after removing only when clicking the "plugins sections"