$string = "bla blа bla";
$tempArray = explode(' ', $string);
foreach($tempArray as $word){
    if(preg_match("/[x41-x7F]/", $word) == 1 && preg_match("/[x80-xFF]/", $word) == 1){
        echo $word," is incorrect";
    }
}

$string = "bla blа bla";
$tempArray = explode(' ', $string);
foreach($tempArray as $word){
    if(preg_match("/[x41-x7F]/", $word) == 1 && !mb_ereg_match("/[x00-x7F]/", $word)){
        echo $word," is incorrect";
    }
}