An error has occurred. 0 Call to undefined function utf8_strtolower()

[vavava]

This is the mistake when creating a category - An error has occurred.      0 Call to undefined function utf8_strtolower()

it is impossible to create even a category please help

[PRO]

"The PHP error
"Fatal error: Call to undefined function utf8_strtolower()" typically occurs because the necessary multibyte string extension (mbstring) is either not installed or not enabled on your server. "