I found a simple way to enchance this plugin for the audience who is familiar to umlauts. In English there's no letters
ä or
ö and such. This keyword-rich URL's plugin strips those letters from URL addresses and that causes a tiny cosmetic problem for some users. So here's a fix to have umlauts "processed":
$topicTitle=str_replace('ä','a',strtolower(utf8_decode($topicTitle)));
$topicTitle=str_replace('ö','o',strtolower(utf8_decode($topicTitle)));
$topicTitle=str_replace('å','a',strtolower(utf8_decode($topicTitle)));
Those lines can be inserted to the PHP file addon_mod_rewrite_1.php, addon_mod_rewrite_2.php or addon_mod_rewrite_3.php. They can be placed right after this line:
function convertTitle($topicTitle){
So this update will make:
ä = a
ö = o
å = a