I looked a little bit at the code and the replaement happens in the Str class of the toolkit: https://github.com/getkirby/toolkit/blob/master/lib/str.php
Through the following array:
static public $ascii = array(
'/Ä/' => 'Ae',
'/æ|ǽ|ä/' => 'ae',
'/œ|ö/' => 'oe',
'/À|Á|Â|Ã|Å|Ǻ|Ā|Ă|Ą|Ǎ|А/' => 'A',
'/à|á|â|ã|å|ǻ|ā|ă|ą|ǎ|ª|а/' => 'a',
'/Б/' => 'B',
'/б/' => 'b',
'/Ç|Ć|Ĉ|Ċ|Č|Ц/' => 'C',
'/ç|ć|ĉ|ċ|č|ц/' => 'c',
'/Ð|Ď|Đ/' => 'Dj',
'/ð|ď|đ/' => 'dj',
'/Д/' => 'D',
'/д/' => 'd',
'/È|É|Ê|Ë|Ē|Ĕ|Ė|Ę|Ě|Е|Ё|Э/' => 'E',
'/è|é|ê|ë|ē|ĕ|ė|ę|ě|е|ё|э/' => 'e',
'/Ф/' => 'F',
'/ƒ|ф/' => 'f',
'/Ĝ|Ğ|Ġ|Ģ|Г/' => 'G',
'/ĝ|ğ|ġ|ģ|г/' => 'g',
'/Ĥ|Ħ|Х/' => 'H',
'/ĥ|ħ|х/' => 'h',
'/Ì|Í|Î|Ï|Ĩ|Ī|Ĭ|Ǐ|Į|İ|И/' => 'I',
'/ì|í|î|ï|ĩ|ī|ĭ|ǐ|į|ı|и/' => 'i',
'/Ĵ|Й/' => 'J',
'/ĵ|й/' => 'j',
'/Ķ|К/' => 'K',
'/ķ|к/' => 'k',
'/Ĺ|Ļ|Ľ|Ŀ|Ł|Л/' => 'L',
'/ĺ|ļ|ľ|ŀ|ł|л/' => 'l',
'/М/' => 'M',
'/м/' => 'm',
'/Ñ|Ń|Ņ|Ň|Н/' => 'N',
'/ñ|ń|ņ|ň|ʼn|н/' => 'n',
'/Ö/' => 'Oe',
'/ö/' => 'oe',
'/Ò|Ó|Ô|Õ|Ō|Ŏ|Ǒ|Ő|Ơ|Ø|Ǿ|О/' => 'O',
'/ò|ó|ô|õ|ō|ŏ|ǒ|ő|ơ|ø|ǿ|º|о/' => 'o',
'/П/' => 'P',
'/п/' => 'p',
'/Ŕ|Ŗ|Ř|Р/' => 'R',
'/ŕ|ŗ|ř|р/' => 'r',
'/Ś|Ŝ|Ş|Ș|Š|С/' => 'S',
'/ś|ŝ|ş|ș|š|ſ|с/' => 's',
'/Ţ|Ț|Ť|Ŧ|Т/' => 'T',
'/ţ|ț|ť|ŧ|т/' => 't',
'/Ü/' => 'Ue',
'/ü/' => 'ue',
'/Ù|Ú|Û|Ũ|Ū|Ŭ|Ů|Ű|Ų|Ư|Ǔ|Ǖ|Ǘ|Ǚ|Ǜ|У/' => 'U',
'/ù|ú|û|ũ|ū|ŭ|ů|ű|ų|ư|ǔ|ǖ|ǘ|ǚ|ǜ|у/' => 'u',
'/В/' => 'V',
'/в/' => 'v',
'/Ý|Ÿ|Ŷ|Ы/' => 'Y',
'/ý|ÿ|ŷ|ы/' => 'y',
'/Ŵ/' => 'W',
'/ŵ/' => 'w',
'/Ź|Ż|Ž|З/' => 'Z',
'/ź|ż|ž|з/' => 'z',
'/Æ|Ǽ/' => 'AE',
'/ß/'=> 'ss',
'/IJ/' => 'IJ',
'/ij/' => 'ij',
'/Œ/' => 'OE',
'/Ч/' => 'Ch',
'/ч/' => 'ch',
'/Ю/' => 'Ju',
'/ю/' => 'ju',
'/Я/' => 'Ja',
'/я/' => 'ja',
'/Ш/' => 'Sh',
'/ш/' => 'sh',
'/Щ/' => 'Shch',
'/щ/' => 'shch',
'/Ж/' => 'Zh',
'/ж/' => 'zh',
);
I haven’t tested anything, but since it is a public static variable maybe you could change it:
str::$ascii = array(); // your array
Not sure if this really works depending on the order and scope of this and when it would get called if you put it e.g. in the config.php
.
Edit: okay, I tried it, but it seems not as simple as have it just redefined in the config.php
. Maybe someone else has an idea where.
Edit2: no actually it does work, it just treats ‘Ä’ as ‘ä’ when replacing, cause all characters are lowered before replaced anyways.