The date format on that page is different than in normal signatures. The month is abbreviated: "sep" for "septembre", "déc" for "décembre".

Apparently the date format used by MediaWiki for French changed in 2005: https://www.mediawiki.org/wiki/Special:Code/MediaWiki/11676 (19f50a04). I'm not sure if it was intentional or a mistake in refactoring, since the commit message doesn't mention anything about changes to French, but changing the code in LanguageFr.php to no longer use getMonthAbbreviation seems like it would do that… (I haven't actually tested it, it would be difficult to figure out all the dependencies of 15-year-old code).

This is the same kind of a problem as T245789. We might not be able to handle discussions from 2005 and earlier on fr.wp. Or we'd need to define alternative timestamp formats for each language.

Those very old timestamp are using abbreviated month names (fév instead of février). I assume fr.wiki switch from short to long month names at some point in the past. Whether or not we try to fix this will probably depend on how long ago that was.

Looking at this page it seems to have been around July 2005: https://fr.wikipedia.org/wiki/Discussion:France/Archive_1, so only conversation from before then will be broken. The chance of someone wanting to reply to a comment that old are pretty low, so we can probably just wontfix this.

Snap, Bartosz.

I looked for details with @Pyb, the format change is observed on the 2005-07-06. I think that this format can be ignored, these discussions have now only a historical value.

Same issue: When new wikis are created they are moved from the incubator (UTC) to something local, in this case (WAT): https://pcm.wikipedia.org/wiki/Tok_abaut_am:Main_Pej