As a Wikidata editor, I want the example Lexeme shown in the info panel on Special:NewLexemeAlpha (soon to be Special:NewLexeme) prefer a message defined on-wiki over the default one defined in the software.

As a Wikidata interface administrator, I don’t want to have to create hundreds of pages in the MediaWiki: namespace just to ensure that users see at least a rudimentary useful example Lexeme on the special page.

Problem:
The example lexeme ID is configured using the wikibaselexeme-newlexeme-info-panel-example-lexeme-id interface message, which defaults to L1 in the extension’s source code (en.json), but which we intend to be overridden on each wiki in the MediaWiki: namespace. Currently on Wikidata, MediaWiki:Wikibaselexeme-newlexeme-info-panel-example-lexeme-id is set to L7 (English noun “cat”), which is a useful example Lexeme for users who look at the page in English. When you load the special page in a language where no specific example lexeme ID has been set in the MediaWiki: namespace yet, we expect the ID to fall back to the English MediaWiki: page, which is still more useful than L1 (Sumerian noun “ama”/“𒂼”). However, this doesn’t happen: apparently, when MediaWiki applies language fallbacks for a message, it only uses the JSON message files and ignores MediaWiki: namespace pages that exist for the fallback languages.

Example:
The special page in Portuguese currently shows L1:

We would like it to show L7 instead, which is likely to be more useful than L1 to Portuguese speakers.

BDD
GIVEN my user interface is in a language other than English
AND no example Lexeme ID has been configured in that specific language yet
WHEN I load Special:NewLexemeAlpha (soon to be Special:NewLexeme)
THEN the info panel shows the example Lexeme defined in the local English message

Acceptance criteria:

• The example lexeme ID falls back to the English message in the MediaWiki: namespace before resorting to the extension’s en.json file.

Note:
We want this to ultimately support the full language fallback chain. This is an intermediate step to improve the situation. See T313599 is for supporting the full fallback chain.