I just checked and this is what I get on English Wikipedia:

That looks fine to me. Can anyone else reproduce it?

@Lydia_Pintscher The problem is not the display of the Afrikaans article but that of the Alemannic arcticle.

Ah doh! Ok that I can reproduce. Thanks!

Screenshot:

Strange. As far as I can tell, this badge was added way back in 2015: https://www.wikidata.org/w/index.php?diff=218895289&oldid=211173639&title=Q5577

And it also shows in Wikidata API requests: https://www.wikidata.org/w/api.php?action=wbgetentities&format=json&ids=Q5577&props=info%7Csitelinks&formatversion=2

However, I confirmed that this problem also exists on other wikis, neither de-wikipedia nor eo-wikipedia are showing the badge in the language switcher.

I noticed that in the API request to SiteMatrix (https://en.wikipedia.org/w/api.php?action=sitematrix&format=json&origin=*&formatversion=2) the value for site for als is empty. Looking at https://en.wikipedia.org/wiki/Special:SiteMatrix it also seems like SiteMatrix thinks that Alemannic Wikipedia does not exist. I'll have a look into where SiteMatrix is getting its data from.

Both on the special page (https://www.mediawiki.org/wiki/Special:SiteMatrix) and the API endpoint (https://en.wikipedia.org/w/api.php?action=sitematrix&format=json&origin=*&formatversion=2) Allemanic is also listed with the code gsw. That is unexpected (to me) and such duplication sounds like a good candidate for causing unexpected behavior. I do not yet know where gsw is coming from in the first place.

The code gsw comes from ISO 639. When Alemannic Wikipedia was created there was no code for Alemannic, so the code als was used. Later the code gsw was introduced in ISO 639. This problem als vs. gsw is known for many years, but so far there have been no technical problems with it.

In T356849#9524314, @Holder wrote:

The code gsw comes from ISO 639. When Alemannic Wikipedia was created there was no code for Alemannic, so the code als was used. Later the code gsw was introduced in ISO 639. This problem als vs. gsw is known for many years, but so far there have been no technical problems with it.

Thanks! Looking at the config, I also found the corresponding info there:

In IntialiseSettings.php:

'wgLanguageCode' => [
	'default' => '$lang',

	# ...

	# Wikis at the wrong domain
	# FIXME: rename these wikis (T21986)
	'alswiki' => 'gsw',
	
	# ...

]

Which links to T21986. That in turn leads to T6793: Rename Alemannic Wikipedia from als.wikipedia to gsw.wikipedia.

@Holder Do you happen to remember when the badges first stopped showing?

Looking at the code in SiteMatrix that deals with this, the change SiteMatrix: Show the actual (non-deprecated) language code for deprecated language codes, merged in August 2023, stands out as potential cause, referencing T172035 and T111876.

Unfortunately, I don't know when the badges disappeared.