This is what I did:
1. go to application / config / foreign_chars.php
2. added
'/š/' => 's', '/đ/' => 'd', '/č/' => 'c', '/ć/' => 'c', '/ž/' => 'z', '/Š/' => 'S', '/Đ/' => 'D', '/Č/' => 'C', '/Ć/' => 'C', '/Ž/' => 'Z',
3. Just call
$clean=convert_accented_characters($string); $url_title = url_title($clean, '_', TRUE);
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