The translations on Transifex were merged with Picard’s code some days ago, but the string for the connection error in the in-built search seems to have been missed (or the source string changed after being pushed to Transifex).

It is the string

<strong>Following error occurred while fetching results:<br><br></strong>Network request error for %s:<br>%s (QT code %d, HTTP code %s)<br>

Located in picard/ui/searchdialog.py:288.