iso-8859-1 to HTML:
<?php
    $str = "Nittenhundreogåttiåtte<br/>\n";
    echo htmlentities($str, ENT_NOQUOTES, 'iso-8859-1');
?>


output:
Nittenhundreog&aring;tti&aring;tte&lt;br/&gt;




UTF-8 to HTML:
<?php
    $str = "NittenhundreogÃ¥ttiÃ¥tte<br/>\n";
    echo htmlentities($str, ENT_NOQUOTES, 'utf-8');
?>


output:
Nittenhundreog&aring;tti&aring;tte&lt;br/&gt;