It appears that advancedsearch-field-preview-sort is a message of the kind that is called "lego" in the MediaWiki jargon: another message is concatenated to it in run time using $.append() instead of being added as a $1 parameter.
This is strongly discouraged, because it causes major difficulties in translation:
For example, this causes this message to appear in the Russian Wikipedia at "Сортировать по релевантность", which is grammatically incorrect. The translators have no way to translate this correctly.
Also, I'm not sure why is the <bdi> tag needed there.
This message must stop using run-time concatenation, and document in qqq what words can after it.