The patch that finally solved T138365 also removed the $1 placeholder from messages. The current messages

• "wikibase-validator-bad-url": "URLs are not allowed to contain certain characters like spaces and square brackets.", and
• "wikibase-validator-url-scheme-missing": "This URL misses a scheme like \"http://\" or \"https://\".",

do not repeat the invalid URLs any more. This is a problem when you are editing a statement with multiple URLs in qualifiers and references. The error message is displayed as a tooltip on the save button (see T138748 for a long-term solution for that).

Proposed short-term solution:

• Check all validator messages and add the $1 placeholders when missing.
• Note that these messages are currently parsed. The bad URLs are displayed as clickable links in the messages. I believe this should be fixed.