Craft.log showing Buggy iconv installed. Will fallback to mbstring
Iconv is a system C library that converts string encodings, and is generally preferable to PHP’s mb_convert_encoding() because it supports significantly more character encodings. However it’s not guaranteed that it will be available, and if it is, some versions of it have a bug that could put it into an infinite loop in certain circumstances. So Craft’s StringHelper::convertToUTF8() checks for those things before using it, and logs if it’s not available or a buggy version is installed, before falling back on mb_convert_encoding().