The method is outlined in the parent ticket.
|mediawiki/extensions/Wikibase||master||+109 -113||Decouple util.highlightSubstring RL module from client and repo|
|Resolved||Ladsgroup||T256054 Copy dependencies of "jquery.wikibase.linkitem" Resource Loader module to Wikibase client JS code|
|Resolved||Ladsgroup||T257475 Decouple util.highlightSubstring RL module from client and repo|
The change works, in that matching substrings are still marked as highlights in the HTML:
<li class="ui-ooMenu-item" dir="auto"><a tabindex="-1"><span class="highlight">En</span>glish (<span class="highlight">en</span>wiki)</a></li>
That said, Wikibase does not define any special styles for the highlight class, and hasn’t done so for quite some time, so the highlighting isn’t visible by default. (In fact I couldn’t find any trace of the class ever being styled in the Git history, but I’m sure it used to be in some submodule or library that I missed. T68433 is an old task for it.) On Wikidata, exactly two users style the class in their common.css (search): User:Kiailandi and User:Hjfocs. I hope they’re happy that we’re still keeping this feature working ^^