Should be mb_stripos. Please add test cases for non-latin character sets.

Doesn't matter much here, but note that this is very inefficient if $string is long. Even if the first character doesn't match, stripos will continue searching through the entire string. If there are many partial matches, this is quite expensive.

You can compare suitable substrings or use regular expressions insteaqd: http://stackoverflow.com/a/7168986/1239832