strcmp and strcasecmp does not work well with multibyte (UTF8) strings and there are no mb_strcmp or mb_strcasecmp - instead look at the wonderful Collator class with method compare (search for Collator above) - supports not only UTF8 but also different national collations (sort orders).
Natural sort is also supported, use setAttribute to set Collator::NUMERIC_COLLATION to Collator::ON.