I have installed language extension and successfully installed on my test store. However, as soon as I have changed the admin language and press save, the admin page crashed, giving 500 error and cannot access at all. Frontend is still accessible.
I have deleted cache, but still not working.
I have contacted the developer, but if anyone has any idea how I could fix this, would be really appreciated.
PHP Fatal error: Uncaught TypeError: Argument 1 passed to iterator_to_array() must implement interface Traversable, null given in /vendor/magento/framework/View/Element/Html/Calendar.php:86