Why doesn't the strtolower and strtoupper function work in PHP?

Question

PHP

I use OPENSERVER. Strtolower and strtoupper are completely ignored. From what I read, I realized that it was necessary to change the language locales. But I have no idea how to do it. The mb_ strtolower and mb_strtoupper functions cause the encoding to crash.
Thanks in advance!

Answer 1

If encoding is UTF-8, then only mb_*
php.net/manual/ru/function.mb-internal-encoding.php