If you are just starting with Drupal 8 then one of the most important things you should know is to enable the debug mode and error reporting on Drupal 8. This is really important for backend as well as frontend developer to the full error on your screen while you are working because you might not know what is the exact issue with the site with just a generic error statement.
While working on Drupal 8 one of the issues you might face is you won't get "Register" link for anonymous user. Here are two simple ways on how to hide "Register" link for users with administrator role.
Here is the quick code snippet of how we can get the current language code, current language name and all enabled languages in Drupal 8 for multilanguage sites.