from a template, use {{<span class="searchmatch">sortkey</span>}}. Within a module, use Module:languages#Language:makeSortKey. For testcases, see Module:<span class="searchmatch">Lana</span>-<span class="searchmatch">sortkey</span>/testcases. makeSortKey(text...
possible to use mw.loadData, then these should be moved there. s["de-Latn-<span class="searchmatch">sortkey</span>"] = { remove_diacritics = c.grave .. c.acute .. c.circ .. c.diaer .. c...
"kkh":{"sort_key":{"<span class="searchmatch">Lana</span>":"<span class="searchmatch">Lana</span>-<span class="searchmatch">sortkey</span>","Thai":"Thai-<span class="searchmatch">sortkey</span>"},"type":"regular","aliases":["Tai Khün","Dai Kun"],"1":"Khün","2":3545044,"3":"tai-swe","4":"<span class="searchmatch">Lana</span>,Thai"}...